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 $73.97   3.264%   $76.3844   $76.38   $76.40   $76.40  
  Purchase #2 $233.50   10.167%   $257.2399   $257.24   $257.25   $257.20  
  Purchase #3 $54.70   10.516%   $60.4523   $60.45   $60.45   $60.50  
  Purchase #4 $200.74   13.275%   $227.3882   $227.39   $227.40   $227.40  
  Purchase #5 $117.95   10.171%   $129.9467   $129.95   $129.95   $129.90  
  Purchase #6 $44.75   8.122%   $48.3846   $48.38   $48.40   $48.40  
  Purchase #7 $243.25   7.140%   $260.6181   $260.62   $260.60   $260.60  
  7 purchase totals = $968.86       $1,060.4142   $1,060.41   $1,060.45   $1,060.40