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 $48.95   11.581%   $54.6189   $54.62   $54.60   $54.60  
  Purchase #2 $111.45   12.505%   $125.3868   $125.39   $125.40   $125.40  
  Purchase #3 $99.27   11.749%   $110.9332   $110.93   $110.95   $110.90  
  Purchase #4 $85.43   9.438%   $93.4929   $93.49   $93.50   $93.50  
  Purchase #5 $32.55   6.543%   $34.6797   $34.68   $34.70   $34.70  
  Purchase #6 $197.97   3.651%   $205.1979   $205.20   $205.20   $205.20  
  Purchase #7 $94.83   5.224%   $99.7839   $99.78   $99.80   $99.80  
  7 purchase totals = $670.45       $724.0933   $724.09   $724.15   $724.10