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 $129.25   10.375%   $142.6597   $142.66   $142.65   $142.70  
  Purchase #2 $36.27   10.785%   $40.1817   $40.18   $40.20   $40.20  
  Purchase #3 $102.70   3.272%   $106.0603   $106.06   $106.05   $106.10  
  Purchase #4 $95.75   7.486%   $102.9178   $102.92   $102.90   $102.90  
  Purchase #5 $132.61   5.533%   $139.9473   $139.95   $139.95   $139.90  
  Purchase #6 $86.26   12.200%   $96.7837   $96.78   $96.80   $96.80  
  Purchase #7 $64.41   3.326%   $66.5523   $66.55   $66.55   $66.60  
  7 purchase totals = $647.25       $695.1028   $695.10   $695.10   $695.20