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 $202.73   12.872%   $228.8254   $228.83   $228.85   $228.80  
  Purchase #2 $207.89   9.398%   $227.4275   $227.43   $227.45   $227.40  
  Purchase #3 $64.53   5.548%   $68.1101   $68.11   $68.10   $68.10  
  Purchase #4 $249.58   7.252%   $267.6795   $267.68   $267.70   $267.70  
  Purchase #5 $51.96   5.559%   $54.8485   $54.85   $54.85   $54.80  
  Purchase #6 $96.93   4.199%   $101.0001   $101.00   $101.00   $101.00  
  Purchase #7 $17.89   6.513%   $19.0552   $19.06   $19.05   $19.10  
  7 purchase totals = $891.51       $966.9463   $966.96   $967.00   $966.90