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 $53.94   11.684%   $60.2423   $60.24   $60.25   $60.20  
  Purchase #2 $137.28   6.843%   $146.6741   $146.67   $146.65   $146.70  
  Purchase #3 $53.75   9.400%   $58.8025   $58.80   $58.80   $58.80  
  Purchase #4 $190.75   13.767%   $217.0106   $217.01   $217.00   $217.00  
  Purchase #5 $141.36   9.405%   $154.6549   $154.65   $154.65   $154.70  
  Purchase #6 $201.36   12.786%   $227.1059   $227.11   $227.10   $227.10  
  Purchase #7 $152.94   11.422%   $170.4088   $170.41   $170.40   $170.40  
  7 purchase totals = $931.38       $1,034.8991   $1,034.89   $1,034.85   $1,034.90