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 $195.95   11.429%   $218.3451   $218.35   $218.35   $218.30  
  Purchase #2 $108.65   6.429%   $115.6351   $115.64   $115.65   $115.60  
  Purchase #3 $243.51   4.746%   $255.067   $255.07   $255.05   $255.10  
  Purchase #4 $216.34   3.659%   $224.2559   $224.26   $224.25   $224.30  
  Purchase #5 $188.37   4.474%   $196.7977   $196.80   $196.80   $196.80  
  Purchase #6 $118.76   4.771%   $124.426   $124.43   $124.45   $124.40  
  Purchase #7 $201.82   13.794%   $229.6591   $229.66   $229.65   $229.70  
  7 purchase totals = $1,273.40       $1,364.1859   $1,364.21   $1,364.20   $1,364.20