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 $195.55   13.370%   $221.695   $221.70   $221.70   $221.70  
  Purchase #2 $164.36   5.224%   $172.9462   $172.95   $172.95   $172.90  
  Purchase #3 $140.93   12.112%   $157.9994   $158.00   $158.00   $158.00  
  Purchase #4 $110.95   7.148%   $118.8807   $118.88   $118.90   $118.90  
  Purchase #5 $61.73   5.207%   $64.9443   $64.94   $64.95   $64.90  
  Purchase #6 $68.30   11.266%   $75.9947   $75.99   $76.00   $76.00  
  Purchase #7 $40.37   10.372%   $44.5572   $44.56   $44.55   $44.60  
  7 purchase totals = $782.19       $857.0175   $857.02   $857.05   $857.00