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 $100.34   5.567%   $105.9259   $105.93   $105.95   $105.90  
  Purchase #2 $10.54   8.524%   $11.4384   $11.44   $11.45   $11.40  
  Purchase #3 $61.43   5.372%   $64.73   $64.73   $64.75   $64.70  
  Purchase #4 $207.25   3.221%   $213.9255   $213.93   $213.95   $213.90  
  Purchase #5 $231.43   4.481%   $241.8004   $241.80   $241.80   $241.80  
  Purchase #6 $199.57   8.132%   $215.799   $215.80   $215.80   $215.80  
  Purchase #7 $131.44   8.485%   $142.5927   $142.59   $142.60   $142.60  
  7 purchase totals = $942.00       $996.2119   $996.22   $996.30   $996.10