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 $244.90   3.698%   $253.9564   $253.96   $253.95   $254.00  
  Purchase #2 $139.48   13.683%   $158.565   $158.57   $158.55   $158.60  
  Purchase #3 $55.91   7.120%   $59.8908   $59.89   $59.90   $59.90  
  Purchase #4 $144.86   11.319%   $161.2567   $161.26   $161.25   $161.30  
  Purchase #5 $58.80   3.819%   $61.0456   $61.05   $61.05   $61.00  
  Purchase #6 $241.79   8.852%   $263.1933   $263.19   $263.20   $263.20  
  Purchase #7 $203.30   11.836%   $227.3626   $227.36   $227.35   $227.40  
  7 purchase totals = $1,089.04       $1,185.2704   $1,185.28   $1,185.25   $1,185.40