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 $86.93   8.129%   $93.9965   $94.00   $94.00   $94.00  
  Purchase #2 $212.89   9.362%   $232.8208   $232.82   $232.80   $232.80  
  Purchase #3 $35.94   7.800%   $38.7433   $38.74   $38.75   $38.70  
  Purchase #4 $13.79   5.531%   $14.5527   $14.55   $14.55   $14.60  
  Purchase #5 $126.66   8.259%   $137.1208   $137.12   $137.10   $137.10  
  Purchase #6 $186.25   12.503%   $209.5368   $209.54   $209.55   $209.50  
  Purchase #7 $34.72   4.694%   $36.3498   $36.35   $36.35   $36.30  
  7 purchase totals = $697.18       $763.1207   $763.12   $763.10   $763.00