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 $25.71   10.528%   $28.4167   $28.42   $28.40   $28.40  
  Purchase #2 $230.68   6.365%   $245.3628   $245.36   $245.35   $245.40  
  Purchase #3 $13.95   4.338%   $14.5552   $14.56   $14.55   $14.60  
  Purchase #4 $171.75   5.508%   $181.21   $181.21   $181.20   $181.20  
  Purchase #5 $68.92   10.376%   $76.0711   $76.07   $76.05   $76.10  
  Purchase #6 $74.46   7.720%   $80.2083   $80.21   $80.20   $80.20  
  Purchase #7 $90.72   12.750%   $102.2868   $102.29   $102.30   $102.30  
  7 purchase totals = $676.19       $728.1109   $728.12   $728.05   $728.20