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 $69.84   9.166%   $76.2415   $76.24   $76.25   $76.20  
  Purchase #2 $46.44   7.521%   $49.9328   $49.93   $49.95   $49.90  
  Purchase #3 $175.98   3.841%   $182.7394   $182.74   $182.75   $182.70  
  Purchase #4 $213.95   7.191%   $229.3351   $229.34   $229.35   $229.30  
  Purchase #5 $245.27   12.149%   $275.0679   $275.07   $275.05   $275.10  
  Purchase #6 $167.81   7.433%   $180.2833   $180.28   $180.30   $180.30  
  Purchase #7 $234.43   4.790%   $245.6592   $245.66   $245.65   $245.70  
  7 purchase totals = $1,153.72       $1,239.2592   $1,239.26   $1,239.30   $1,239.20