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 $202.93   10.182%   $223.5923   $223.59   $223.60   $223.60  
  Purchase #2 $72.96   5.167%   $76.7298   $76.73   $76.75   $76.70  
  Purchase #3 $35.70   3.684%   $37.0152   $37.02   $37.00   $37.00  
  Purchase #4 $58.84   10.223%   $64.8552   $64.86   $64.85   $64.90  
  Purchase #5 $148.74   8.503%   $161.3874   $161.39   $161.40   $161.40  
  Purchase #6 $73.60   4.596%   $76.9827   $76.98   $77.00   $77.00  
  Purchase #7 $44.44   4.307%   $46.354   $46.35   $46.35   $46.40  
  7 purchase totals = $637.21       $686.9166   $686.92   $686.95   $687.00