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 $210.91   6.374%   $224.3534   $224.35   $224.35   $224.40  
  Purchase #2 $24.61   9.253%   $26.8872   $26.89   $26.90   $26.90  
  Purchase #3 $245.34   12.223%   $275.3279   $275.33   $275.35   $275.30  
  Purchase #4 $177.34   13.685%   $201.609   $201.61   $201.60   $201.60  
  Purchase #5 $89.77   3.277%   $92.7118   $92.71   $92.70   $92.70  
  Purchase #6 $125.37   5.294%   $132.0071   $132.01   $132.00   $132.00  
  Purchase #7 $154.76   3.638%   $160.3902   $160.39   $160.40   $160.40  
  7 purchase totals = $1,028.10       $1,113.2866   $1,113.29   $1,113.30   $1,113.30