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 $41.68   6.137%   $44.2379   $44.24   $44.25   $44.20  
  Purchase #2 $234.43   5.323%   $246.9087   $246.91   $246.90   $246.90  
  Purchase #3 $80.26   4.782%   $84.098   $84.10   $84.10   $84.10  
  Purchase #4 $51.73   6.491%   $55.0878   $55.09   $55.10   $55.10  
  Purchase #5 $132.26   5.586%   $139.648   $139.65   $139.65   $139.60  
  Purchase #6 $40.97   12.517%   $46.0982   $46.10   $46.10   $46.10  
  Purchase #7 $121.62   10.542%   $134.4412   $134.44   $134.45   $134.40  
  7 purchase totals = $702.95       $750.5198   $750.53   $750.55   $750.40