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 $60.66   7.549%   $65.2392   $65.24   $65.25   $65.20  
  Purchase #2 $207.85   11.873%   $232.528   $232.53   $232.55   $232.50  
  Purchase #3 $185.79   6.579%   $198.0131   $198.01   $198.00   $198.00  
  Purchase #4 $27.62   6.394%   $29.386   $29.39   $29.40   $29.40  
  Purchase #5 $10.69   5.592%   $11.2878   $11.29   $11.30   $11.30  
  Purchase #6 $111.94   13.209%   $126.7262   $126.73   $126.75   $126.70  
  Purchase #7 $10.48   8.598%   $11.3811   $11.38   $11.40   $11.40  
  7 purchase totals = $615.03       $674.5614   $674.57   $674.65   $674.50