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 $237.38   3.676%   $246.1061   $246.11   $246.10   $246.10  
  Purchase #2 $8.34   13.321%   $9.451   $9.45   $9.45   $9.50  
  Purchase #3 $60.54   6.344%   $64.3807   $64.38   $64.40   $64.40  
  Purchase #4 $63.96   6.623%   $68.1961   $68.20   $68.20   $68.20  
  Purchase #5 $84.72   8.247%   $91.7069   $91.71   $91.70   $91.70  
  Purchase #6 $30.71   7.468%   $33.0034   $33.00   $33.00   $33.00  
  Purchase #7 $222.76   10.614%   $246.4037   $246.40   $246.40   $246.40  
  7 purchase totals = $708.41       $759.2479   $759.25   $759.25   $759.30