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 $247.62   5.268%   $260.6646   $260.66   $260.65   $260.70  
  Purchase #2 $62.86   6.686%   $67.0628   $67.06   $67.05   $67.10  
  Purchase #3 $182.93   12.788%   $206.3231   $206.32   $206.30   $206.30  
  Purchase #4 $19.53   3.495%   $20.2126   $20.21   $20.20   $20.20  
  Purchase #5 $58.88   7.572%   $63.3384   $63.34   $63.35   $63.30  
  Purchase #6 $65.29   4.457%   $68.2   $68.20   $68.20   $68.20  
  Purchase #7 $5.43   10.540%   $6.0023   $6.00   $6.00   $6.00  
  7 purchase totals = $642.54       $691.8038   $691.79   $691.75   $691.80