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 $233.93   11.573%   $261.0027   $261.00   $261.00   $261.00  
  Purchase #2 $139.60   5.264%   $146.9485   $146.95   $146.95   $146.90  
  Purchase #3 $218.54   8.614%   $237.365   $237.37   $237.35   $237.40  
  Purchase #4 $94.45   8.439%   $102.4206   $102.42   $102.40   $102.40  
  Purchase #5 $234.27   3.758%   $243.0739   $243.07   $243.05   $243.10  
  Purchase #6 $100.77   11.257%   $112.1137   $112.11   $112.10   $112.10  
  Purchase #7 $222.74   13.368%   $252.5159   $252.52   $252.50   $252.50  
  7 purchase totals = $1,244.30       $1,355.4403   $1,355.44   $1,355.35   $1,355.40