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 $53.35   5.323%   $56.1898   $56.19   $56.20   $56.20  
  Purchase #2 $130.73   10.718%   $144.7416   $144.74   $144.75   $144.70  
  Purchase #3 $127.64   9.478%   $139.7377   $139.74   $139.75   $139.70  
  Purchase #4 $156.48   6.279%   $166.3054   $166.31   $166.30   $166.30  
  Purchase #5 $178.68   8.667%   $194.1662   $194.17   $194.15   $194.20  
  Purchase #6 $195.68   5.254%   $205.961   $205.96   $205.95   $206.00  
  Purchase #7 $101.60   11.487%   $113.2708   $113.27   $113.25   $113.30  
  7 purchase totals = $944.16       $1,020.3725   $1,020.38   $1,020.35   $1,020.40