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 $66.35   7.313%   $71.2022   $71.20   $71.20   $71.20  
  Purchase #2 $175.62   13.230%   $198.8545   $198.85   $198.85   $198.90  
  Purchase #3 $117.35   7.348%   $125.9729   $125.97   $125.95   $126.00  
  Purchase #4 $232.90   11.491%   $259.6625   $259.66   $259.65   $259.70  
  Purchase #5 $154.53   10.361%   $170.5409   $170.54   $170.55   $170.50  
  Purchase #6 $199.82   7.289%   $214.3849   $214.38   $214.40   $214.40  
  Purchase #7 $123.39   6.658%   $131.6053   $131.61   $131.60   $131.60  
  7 purchase totals = $1,069.96       $1,172.2232   $1,172.21   $1,172.20   $1,172.30