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 $135.81   8.812%   $147.7776   $147.78   $147.80   $147.80  
  Purchase #2 $180.60   12.505%   $203.184   $203.18   $203.20   $203.20  
  Purchase #3 $104.66   3.196%   $108.0049   $108.00   $108.00   $108.00  
  Purchase #4 $176.86   3.736%   $183.4675   $183.47   $183.45   $183.50  
  Purchase #5 $40.41   12.854%   $45.6043   $45.60   $45.60   $45.60  
  Purchase #6 $155.32   10.810%   $172.1101   $172.11   $172.10   $172.10  
  Purchase #7 $46.87   12.659%   $52.8033   $52.80   $52.80   $52.80  
  7 purchase totals = $840.53       $912.9517   $912.94   $912.95   $913.00