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 $222.67   8.232%   $241.0002   $241.00   $241.00   $241.00  
  Purchase #2 $23.77   9.175%   $25.9509   $25.95   $25.95   $26.00  
  Purchase #3 $107.64   5.429%   $113.4838   $113.48   $113.50   $113.50  
  Purchase #4 $128.76   3.510%   $133.2795   $133.28   $133.30   $133.30  
  Purchase #5 $89.36   11.337%   $99.4907   $99.49   $99.50   $99.50  
  Purchase #6 $141.82   4.639%   $148.399   $148.40   $148.40   $148.40  
  Purchase #7 $158.80   3.716%   $164.701   $164.70   $164.70   $164.70  
  7 purchase totals = $872.82       $926.3051   $926.30   $926.35   $926.40