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 $206.51   12.803%   $232.9495   $232.95   $232.95   $232.90  
  Purchase #2 $236.85   12.443%   $266.3212   $266.32   $266.30   $266.30  
  Purchase #3 $145.69   9.104%   $158.9536   $158.95   $158.95   $159.00  
  Purchase #4 $170.39   6.846%   $182.0549   $182.05   $182.05   $182.10  
  Purchase #5 $176.96   13.189%   $200.2993   $200.30   $200.30   $200.30  
  Purchase #6 $151.28   11.198%   $168.2203   $168.22   $168.20   $168.20  
  Purchase #7 $6.95   13.175%   $7.8657   $7.87   $7.85   $7.90  
  7 purchase totals = $1,094.63       $1,216.6645   $1,216.66   $1,216.60   $1,216.70