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 $31.95   10.716%   $35.3738   $35.37   $35.35   $35.40  
  Purchase #2 $181.78   5.716%   $192.1705   $192.17   $192.15   $192.20  
  Purchase #3 $232.94   4.202%   $242.7281   $242.73   $242.75   $242.70  
  Purchase #4 $60.50   7.513%   $65.0454   $65.05   $65.05   $65.00  
  Purchase #5 $179.30   8.365%   $194.2984   $194.30   $194.30   $194.30  
  Purchase #6 $145.47   11.282%   $161.8819   $161.88   $161.90   $161.90  
  Purchase #7 $10.72   6.722%   $11.4406   $11.44   $11.45   $11.40  
  7 purchase totals = $842.66       $902.9387   $902.94   $902.95   $902.90