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 $187.25   8.150%   $202.5109   $202.51   $202.50   $202.50  
  Purchase #2 $36.88   9.526%   $40.3932   $40.39   $40.40   $40.40  
  Purchase #3 $138.35   9.501%   $151.4946   $151.49   $151.50   $151.50  
  Purchase #4 $110.56   8.472%   $119.9266   $119.93   $119.95   $119.90  
  Purchase #5 $171.38   10.210%   $188.8779   $188.88   $188.90   $188.90  
  Purchase #6 $133.32   12.138%   $149.5024   $149.50   $149.50   $149.50  
  Purchase #7 $218.98   12.382%   $246.0941   $246.09   $246.10   $246.10  
  7 purchase totals = $996.72       $1,098.7997   $1,098.79   $1,098.85   $1,098.80