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 $64.80   10.599%   $71.6682   $71.67   $71.65   $71.70  
  Purchase #2 $101.92   3.728%   $105.7196   $105.72   $105.70   $105.70  
  Purchase #3 $205.29   5.689%   $216.9689   $216.97   $216.95   $217.00  
  Purchase #4 $153.92   8.433%   $166.9001   $166.90   $166.90   $166.90  
  Purchase #5 $112.87   4.232%   $117.6467   $117.65   $117.65   $117.60  
  Purchase #6 $213.61   7.238%   $229.0711   $229.07   $229.05   $229.10  
  Purchase #7 $53.62   11.103%   $59.5734   $59.57   $59.55   $59.60  
  7 purchase totals = $906.03       $967.5480   $967.55   $967.45   $967.60