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 $58.94   5.126%   $61.9613   $61.96   $61.95   $62.00  
  Purchase #2 $144.67   9.338%   $158.1793   $158.18   $158.20   $158.20  
  Purchase #3 $167.46   11.369%   $186.4985   $186.50   $186.50   $186.50  
  Purchase #4 $186.89   12.433%   $210.126   $210.13   $210.15   $210.10  
  Purchase #5 $7.50   9.304%   $8.1978   $8.20   $8.20   $8.20  
  Purchase #6 $68.96   8.530%   $74.8423   $74.84   $74.85   $74.80  
  Purchase #7 $231.62   8.575%   $251.4814   $251.48   $251.50   $251.50  
  7 purchase totals = $866.04       $951.2866   $951.29   $951.35   $951.30