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 $56.35   11.777%   $62.9863   $62.99   $63.00   $63.00  
  Purchase #2 $163.83   11.272%   $182.2969   $182.30   $182.30   $182.30  
  Purchase #3 $132.57   12.156%   $148.6852   $148.69   $148.70   $148.70  
  Purchase #4 $60.70   5.315%   $63.9262   $63.93   $63.95   $63.90  
  Purchase #5 $191.33   3.375%   $197.7874   $197.79   $197.80   $197.80  
  Purchase #6 $136.37   11.814%   $152.4808   $152.48   $152.50   $152.50  
  Purchase #7 $199.92   12.664%   $225.2379   $225.24   $225.25   $225.20  
  7 purchase totals = $941.07       $1,033.4007   $1,033.42   $1,033.50   $1,033.40