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 $83.73   12.246%   $93.9836   $93.98   $94.00   $94.00  
  Purchase #2 $113.50   3.279%   $117.2217   $117.22   $117.20   $117.20  
  Purchase #3 $237.25   10.240%   $261.5444   $261.54   $261.55   $261.50  
  Purchase #4 $175.46   12.333%   $197.0995   $197.10   $197.10   $197.10  
  Purchase #5 $15.50   11.139%   $17.2265   $17.23   $17.25   $17.20  
  Purchase #6 $81.79   11.784%   $91.4281   $91.43   $91.45   $91.40  
  Purchase #7 $192.26   11.685%   $214.7256   $214.73   $214.75   $214.70  
  7 purchase totals = $899.49       $993.2294   $993.23   $993.30   $993.10