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 $233.32   5.590%   $246.3626   $246.36   $246.35   $246.40  
  Purchase #2 $177.68   9.592%   $194.7231   $194.72   $194.70   $194.70  
  Purchase #3 $98.32   7.313%   $105.5101   $105.51   $105.50   $105.50  
  Purchase #4 $19.31   10.318%   $21.3024   $21.30   $21.30   $21.30  
  Purchase #5 $65.99   7.292%   $70.802   $70.80   $70.80   $70.80  
  Purchase #6 $148.45   5.695%   $156.9042   $156.90   $156.90   $156.90  
  Purchase #7 $140.27   3.862%   $145.6872   $145.69   $145.70   $145.70  
  7 purchase totals = $883.34       $941.2916   $941.28   $941.25   $941.30