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 $133.79   13.537%   $151.9012   $151.90   $151.90   $151.90  
  Purchase #2 $187.87   3.667%   $194.7592   $194.76   $194.75   $194.80  
  Purchase #3 $196.99   13.737%   $224.0505   $224.05   $224.05   $224.10  
  Purchase #4 $95.64   5.722%   $101.1125   $101.11   $101.10   $101.10  
  Purchase #5 $166.52   9.307%   $182.018   $182.02   $182.00   $182.00  
  Purchase #6 $48.54   10.349%   $53.5634   $53.56   $53.55   $53.60  
  Purchase #7 $45.43   4.669%   $47.5511   $47.55   $47.55   $47.60  
  7 purchase totals = $874.78       $954.9559   $954.95   $954.90   $955.10