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 $130.91   11.594%   $146.0877   $146.09   $146.10   $146.10  
  Purchase #2 $84.41   12.147%   $94.6633   $94.66   $94.65   $94.70  
  Purchase #3 $89.43   5.191%   $94.0723   $94.07   $94.05   $94.10  
  Purchase #4 $182.93   10.407%   $201.9675   $201.97   $201.95   $202.00  
  Purchase #5 $93.39   8.426%   $101.259   $101.26   $101.25   $101.30  
  Purchase #6 $49.66   3.262%   $51.2799   $51.28   $51.30   $51.30  
  Purchase #7 $135.92   7.220%   $145.7334   $145.73   $145.75   $145.70  
  7 purchase totals = $766.65       $835.0631   $835.06   $835.05   $835.20