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 $73.68   3.659%   $76.376   $76.38   $76.40   $76.40  
  Purchase #2 $110.67   12.638%   $124.6565   $124.66   $124.65   $124.70  
  Purchase #3 $49.79   6.804%   $53.1777   $53.18   $53.20   $53.20  
  Purchase #4 $206.74   3.172%   $213.2978   $213.30   $213.30   $213.30  
  Purchase #5 $67.42   12.768%   $76.0282   $76.03   $76.05   $76.00  
  Purchase #6 $229.57   13.418%   $260.3737   $260.37   $260.35   $260.40  
  Purchase #7 $137.49   4.188%   $143.2481   $143.25   $143.25   $143.20  
  7 purchase totals = $875.36       $947.1580   $947.17   $947.20   $947.20