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 $59.73   5.461%   $62.9919   $62.99   $63.00   $63.00  
  Purchase #2 $101.39   6.218%   $107.6944   $107.69   $107.70   $107.70  
  Purchase #3 $23.88   4.780%   $25.0215   $25.02   $25.00   $25.00  
  Purchase #4 $243.86   9.590%   $267.2462   $267.25   $267.25   $267.20  
  Purchase #5 $61.75   11.328%   $68.745   $68.75   $68.75   $68.70  
  Purchase #6 $35.60   11.562%   $39.7161   $39.72   $39.70   $39.70  
  Purchase #7 $21.75   9.159%   $23.7421   $23.74   $23.75   $23.70  
  7 purchase totals = $547.96       $595.1572   $595.16   $595.15   $595.00