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 $53.57   11.772%   $59.8763   $59.88   $59.90   $59.90  
  Purchase #2 $187.44   4.154%   $195.2263   $195.23   $195.25   $195.20  
  Purchase #3 $148.90   11.742%   $166.3838   $166.38   $166.40   $166.40  
  Purchase #4 $246.74   4.269%   $257.2733   $257.27   $257.25   $257.30  
  Purchase #5 $20.53   7.144%   $21.9967   $22.00   $22.00   $22.00  
  Purchase #6 $101.99   3.361%   $105.4179   $105.42   $105.40   $105.40  
  Purchase #7 $11.47   10.268%   $12.6477   $12.65   $12.65   $12.60  
  7 purchase totals = $770.64       $818.8220   $818.83   $818.85   $818.80