Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.41   8.814%   $214.8097   $214.81   $214.80   $214.80  
  Purchase #2 $125.98   12.735%   $142.0236   $142.02   $142.00   $142.00  
  Purchase #3 $117.78   6.445%   $125.3709   $125.37   $125.35   $125.40  
  Purchase #4 $213.52   7.528%   $229.5938   $229.59   $229.60   $229.60  
  Purchase #5 $125.64   7.736%   $135.3595   $135.36   $135.35   $135.40  
  Purchase #6 $142.51   12.516%   $160.3466   $160.35   $160.35   $160.30  
  Purchase #7 $239.75   6.698%   $255.8085   $255.81   $255.80   $255.80  
  7 purchase totals = $1,162.59       $1,263.3126   $1,263.31   $1,263.25   $1,263.30