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 $194.49   13.212%   $220.186   $220.19   $220.20   $220.20  
  Purchase #2 $98.52   12.338%   $110.6754   $110.68   $110.70   $110.70  
  Purchase #3 $73.75   10.116%   $81.2106   $81.21   $81.20   $81.20  
  Purchase #4 $46.36   13.607%   $52.6682   $52.67   $52.65   $52.70  
  Purchase #5 $115.96   7.281%   $124.403   $124.40   $124.40   $124.40  
  Purchase #6 $239.47   9.583%   $262.4184   $262.42   $262.40   $262.40  
  Purchase #7 $98.62   6.844%   $105.3696   $105.37   $105.35   $105.40  
  7 purchase totals = $867.17       $956.9312   $956.94   $956.90   $957.00