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 $91.76   5.826%   $97.1059   $97.11   $97.10   $97.10  
  Purchase #2 $218.65   8.518%   $237.2746   $237.27   $237.25   $237.30  
  Purchase #3 $71.78   5.533%   $75.7516   $75.75   $75.75   $75.80  
  Purchase #4 $35.71   8.392%   $38.7068   $38.71   $38.70   $38.70  
  Purchase #5 $59.65   10.767%   $66.0725   $66.07   $66.05   $66.10  
  Purchase #6 $245.93   3.834%   $255.359   $255.36   $255.35   $255.40  
  Purchase #7 $39.98   6.194%   $42.4564   $42.46   $42.45   $42.50  
  7 purchase totals = $763.46       $812.7268   $812.73   $812.65   $812.90