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 $88.27   9.513%   $96.6671   $96.67   $96.65   $96.70  
  Purchase #2 $100.56   3.293%   $103.8714   $103.87   $103.85   $103.90  
  Purchase #3 $213.62   5.176%   $224.677   $224.68   $224.70   $224.70  
  Purchase #4 $116.93   13.779%   $133.0418   $133.04   $133.05   $133.00  
  Purchase #5 $32.90   4.646%   $34.4285   $34.43   $34.45   $34.40  
  Purchase #6 $17.51   6.183%   $18.5926   $18.59   $18.60   $18.60  
  Purchase #7 $140.69   5.689%   $148.6939   $148.69   $148.70   $148.70  
  7 purchase totals = $710.48       $759.9723   $759.97   $760.00   $760.00