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 $170.55   7.106%   $182.6693   $182.67   $182.65   $182.70  
  Purchase #2 $52.47   10.205%   $57.8246   $57.82   $57.80   $57.80  
  Purchase #3 $101.96   8.622%   $110.751   $110.75   $110.75   $110.80  
  Purchase #4 $242.85   11.205%   $270.0613   $270.06   $270.05   $270.10  
  Purchase #5 $237.79   9.868%   $261.2551   $261.26   $261.25   $261.30  
  Purchase #6 $216.45   5.370%   $228.0734   $228.07   $228.05   $228.10  
  Purchase #7 $210.55   13.164%   $238.2668   $238.27   $238.25   $238.30  
  7 purchase totals = $1,232.62       $1,348.9015   $1,348.90   $1,348.80   $1,349.10