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 $58.35   9.796%   $64.066   $64.07   $64.05   $64.10  
  Purchase #2 $230.62   8.151%   $249.4178   $249.42   $249.40   $249.40  
  Purchase #3 $39.31   12.697%   $44.3012   $44.30   $44.30   $44.30  
  Purchase #4 $148.58   8.576%   $161.3222   $161.32   $161.30   $161.30  
  Purchase #5 $139.64   3.771%   $144.9058   $144.91   $144.90   $144.90  
  Purchase #6 $84.80   13.365%   $96.1335   $96.13   $96.15   $96.10  
  Purchase #7 $8.75   5.408%   $9.2232   $9.22   $9.20   $9.20  
  7 purchase totals = $710.05       $769.3697   $769.37   $769.30   $769.30