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 $237.92   7.190%   $255.0264   $255.03   $255.05   $255.00  
  Purchase #2 $94.66   9.227%   $103.3943   $103.39   $103.40   $103.40  
  Purchase #3 $77.77   5.823%   $82.2985   $82.30   $82.30   $82.30  
  Purchase #4 $193.53   4.328%   $201.906   $201.91   $201.90   $201.90  
  Purchase #5 $212.76   11.556%   $237.3465   $237.35   $237.35   $237.30  
  Purchase #6 $198.76   5.363%   $209.4195   $209.42   $209.40   $209.40  
  Purchase #7 $12.93   5.265%   $13.6108   $13.61   $13.60   $13.60  
  7 purchase totals = $1,028.33       $1,103.0020   $1,103.01   $1,103.00   $1,102.90