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 $42.39   9.327%   $46.3437   $46.34   $46.35   $46.30  
  Purchase #2 $154.69   6.313%   $164.4556   $164.46   $164.45   $164.50  
  Purchase #3 $166.54   3.583%   $172.5071   $172.51   $172.50   $172.50  
  Purchase #4 $185.26   5.377%   $195.2214   $195.22   $195.20   $195.20  
  Purchase #5 $185.47   6.497%   $197.52   $197.52   $197.50   $197.50  
  Purchase #6 $168.98   6.402%   $179.7981   $179.80   $179.80   $179.80  
  Purchase #7 $66.83   5.299%   $70.3713   $70.37   $70.35   $70.40  
  7 purchase totals = $970.16       $1,026.2172   $1,026.22   $1,026.15   $1,026.20