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 $48.77   10.602%   $53.9406   $53.94   $53.95   $53.90  
  Purchase #2 $67.34   9.688%   $73.8639   $73.86   $73.85   $73.90  
  Purchase #3 $138.38   6.462%   $147.3221   $147.32   $147.30   $147.30  
  Purchase #4 $207.54   8.285%   $224.7347   $224.73   $224.75   $224.70  
  Purchase #5 $65.68   6.147%   $69.7173   $69.72   $69.70   $69.70  
  Purchase #6 $103.48   8.727%   $112.5107   $112.51   $112.50   $112.50  
  Purchase #7 $249.74   11.863%   $279.3667   $279.37   $279.35   $279.40  
  7 purchase totals = $880.93       $961.4560   $961.45   $961.40   $961.40