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 $234.39   6.523%   $249.6793   $249.68   $249.70   $249.70  
  Purchase #2 $184.51   3.284%   $190.5693   $190.57   $190.55   $190.60  
  Purchase #3 $67.71   3.313%   $69.9532   $69.95   $69.95   $70.00  
  Purchase #4 $151.34   4.485%   $158.1276   $158.13   $158.15   $158.10  
  Purchase #5 $91.25   11.784%   $102.0029   $102.00   $102.00   $102.00  
  Purchase #6 $161.79   9.422%   $177.0339   $177.03   $177.05   $177.00  
  Purchase #7 $233.72   7.125%   $250.3726   $250.37   $250.35   $250.40  
  7 purchase totals = $1,124.71       $1,197.7388   $1,197.73   $1,197.75   $1,197.80