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 $70.98   10.596%   $78.501   $78.50   $78.50   $78.50  
  Purchase #2 $94.54   9.259%   $103.2935   $103.29   $103.30   $103.30  
  Purchase #3 $193.42   6.820%   $206.6112   $206.61   $206.60   $206.60  
  Purchase #4 $62.89   8.385%   $68.1633   $68.16   $68.15   $68.20  
  Purchase #5 $242.91   6.516%   $258.738   $258.74   $258.75   $258.70  
  Purchase #6 $125.27   11.131%   $139.2138   $139.21   $139.20   $139.20  
  Purchase #7 $250.86   5.558%   $264.8028   $264.80   $264.80   $264.80  
  7 purchase totals = $1,040.87       $1,119.3236   $1,119.31   $1,119.30   $1,119.30