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 $226.28   10.612%   $250.2928   $250.29   $250.30   $250.30  
  Purchase #2 $209.56   12.237%   $235.2039   $235.20   $235.20   $235.20  
  Purchase #3 $213.77   3.750%   $221.7864   $221.79   $221.80   $221.80  
  Purchase #4 $239.89   9.770%   $263.3273   $263.33   $263.35   $263.30  
  Purchase #5 $113.63   3.142%   $117.2003   $117.20   $117.20   $117.20  
  Purchase #6 $151.68   4.458%   $158.4419   $158.44   $158.45   $158.40  
  Purchase #7 $168.27   13.236%   $190.5422   $190.54   $190.55   $190.50  
  7 purchase totals = $1,323.08       $1,436.7948   $1,436.79   $1,436.85   $1,436.70