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 $88.81   10.704%   $98.3162   $98.32   $98.30   $98.30  
  Purchase #2 $6.35   7.812%   $6.8461   $6.85   $6.85   $6.80  
  Purchase #3 $168.77   4.530%   $176.4153   $176.42   $176.40   $176.40  
  Purchase #4 $147.86   6.863%   $158.0076   $158.01   $158.00   $158.00  
  Purchase #5 $73.69   6.661%   $78.5985   $78.60   $78.60   $78.60  
  Purchase #6 $194.83   3.480%   $201.6101   $201.61   $201.60   $201.60  
  Purchase #7 $242.27   9.484%   $265.2469   $265.25   $265.25   $265.20  
  7 purchase totals = $922.58       $985.0407   $985.06   $985.00   $984.90