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 $214.88   7.405%   $230.7919   $230.79   $230.80   $230.80  
  Purchase #2 $162.74   8.247%   $176.1612   $176.16   $176.15   $176.20  
  Purchase #3 $102.51   8.871%   $111.6037   $111.60   $111.60   $111.60  
  Purchase #4 $175.94   4.732%   $184.2655   $184.27   $184.25   $184.30  
  Purchase #5 $181.91   10.841%   $201.6309   $201.63   $201.65   $201.60  
  Purchase #6 $45.52   6.241%   $48.3609   $48.36   $48.35   $48.40  
  Purchase #7 $48.54   4.465%   $50.7073   $50.71   $50.70   $50.70  
  7 purchase totals = $932.04       $1,003.5214   $1,003.52   $1,003.50   $1,003.60