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 $211.44   10.819%   $234.3157   $234.32   $234.30   $234.30  
  Purchase #2 $207.38   10.782%   $229.7397   $229.74   $229.75   $229.70  
  Purchase #3 $16.47   10.534%   $18.2049   $18.20   $18.20   $18.20  
  Purchase #4 $178.76   10.414%   $197.3761   $197.38   $197.40   $197.40  
  Purchase #5 $18.65   6.515%   $19.865   $19.87   $19.85   $19.90  
  Purchase #6 $50.44   6.165%   $53.5496   $53.55   $53.55   $53.50  
  Purchase #7 $218.34   11.767%   $244.0321   $244.03   $244.05   $244.00  
  7 purchase totals = $901.48       $997.0831   $997.09   $997.10   $997.00