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 $214.57   13.789%   $244.1571   $244.16   $244.15   $244.20  
  Purchase #2 $97.91   8.234%   $105.9719   $105.97   $105.95   $106.00  
  Purchase #3 $60.38   12.698%   $68.0471   $68.05   $68.05   $68.00  
  Purchase #4 $143.47   4.457%   $149.8645   $149.86   $149.85   $149.90  
  Purchase #5 $130.57   7.371%   $140.1943   $140.19   $140.20   $140.20  
  Purchase #6 $155.71   10.298%   $171.745   $171.75   $171.75   $171.70  
  Purchase #7 $20.90   10.171%   $23.0257   $23.03   $23.05   $23.00  
  7 purchase totals = $823.51       $903.0056   $903.01   $903.00   $903.00