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 $60.65   7.106%   $64.9598   $64.96   $64.95   $65.00  
  Purchase #2 $74.64   9.496%   $81.7278   $81.73   $81.75   $81.70  
  Purchase #3 $212.52   8.589%   $230.7733   $230.77   $230.75   $230.80  
  Purchase #4 $59.77   5.361%   $62.9743   $62.97   $62.95   $63.00  
  Purchase #5 $60.52   13.534%   $68.7108   $68.71   $68.70   $68.70  
  Purchase #6 $125.55   13.688%   $142.7353   $142.74   $142.75   $142.70  
  Purchase #7 $63.70   3.518%   $65.941   $65.94   $65.95   $65.90  
  7 purchase totals = $657.35       $717.8223   $717.82   $717.80   $717.80