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 $233.77   8.789%   $254.316   $254.32   $254.30   $254.30  
  Purchase #2 $186.61   12.786%   $210.47   $210.47   $210.45   $210.50  
  Purchase #3 $5.95   10.291%   $6.5623   $6.56   $6.55   $6.60  
  Purchase #4 $58.82   6.476%   $62.6292   $62.63   $62.65   $62.60  
  Purchase #5 $77.75   12.802%   $87.7036   $87.70   $87.70   $87.70  
  Purchase #6 $138.47   9.650%   $151.8324   $151.83   $151.85   $151.80  
  Purchase #7 $193.86   7.278%   $207.9691   $207.97   $207.95   $208.00  
  7 purchase totals = $895.23       $981.4826   $981.48   $981.45   $981.50