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 $53.33   12.132%   $59.8   $59.80   $59.80   $59.80  
  Purchase #2 $228.71   4.258%   $238.4485   $238.45   $238.45   $238.40  
  Purchase #3 $65.45   4.232%   $68.2198   $68.22   $68.20   $68.20  
  Purchase #4 $140.93   8.478%   $152.878   $152.88   $152.90   $152.90  
  Purchase #5 $229.79   13.867%   $261.655   $261.66   $261.65   $261.70  
  Purchase #6 $63.56   8.775%   $69.1374   $69.14   $69.15   $69.10  
  Purchase #7 $164.62   3.384%   $170.1907   $170.19   $170.20   $170.20  
  7 purchase totals = $946.39       $1,020.3294   $1,020.34   $1,020.35   $1,020.30