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 $114.49   8.184%   $123.8599   $123.86   $123.85   $123.90  
  Purchase #2 $117.53   9.630%   $128.8481   $128.85   $128.85   $128.80  
  Purchase #3 $43.70   11.283%   $48.6307   $48.63   $48.65   $48.60  
  Purchase #4 $149.44   7.773%   $161.056   $161.06   $161.05   $161.10  
  Purchase #5 $91.54   10.257%   $100.9293   $100.93   $100.95   $100.90  
  Purchase #6 $157.33   13.431%   $178.461   $178.46   $178.45   $178.50  
  Purchase #7 $183.46   4.756%   $192.1854   $192.19   $192.20   $192.20  
  7 purchase totals = $857.49       $933.9704   $933.98   $934.00   $934.00