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 $215.57   12.614%   $242.762   $242.76   $242.75   $242.80  
  Purchase #2 $99.32   4.637%   $103.9255   $103.93   $103.95   $103.90  
  Purchase #3 $34.90   7.795%   $37.6205   $37.62   $37.60   $37.60  
  Purchase #4 $26.59   6.621%   $28.3505   $28.35   $28.35   $28.40  
  Purchase #5 $82.37   13.264%   $93.2956   $93.30   $93.30   $93.30  
  Purchase #6 $27.75   7.701%   $29.887   $29.89   $29.90   $29.90  
  Purchase #7 $141.99   13.627%   $161.339   $161.34   $161.35   $161.30  
  7 purchase totals = $628.49       $697.1801   $697.19   $697.20   $697.20