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 $216.34   11.285%   $240.754   $240.75   $240.75   $240.80  
  Purchase #2 $173.61   12.643%   $195.5595   $195.56   $195.55   $195.60  
  Purchase #3 $44.42   9.473%   $48.6279   $48.63   $48.65   $48.60  
  Purchase #4 $76.42   6.160%   $81.1275   $81.13   $81.15   $81.10  
  Purchase #5 $205.36   6.636%   $218.9877   $218.99   $219.00   $219.00  
  Purchase #6 $31.89   3.248%   $32.9258   $32.93   $32.95   $32.90  
  Purchase #7 $207.37   6.421%   $220.6852   $220.69   $220.70   $220.70  
  7 purchase totals = $955.41       $1,038.6676   $1,038.68   $1,038.75   $1,038.70