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 $195.52   13.571%   $222.054   $222.05   $222.05   $222.10  
  Purchase #2 $199.94   4.494%   $208.9253   $208.93   $208.95   $208.90  
  Purchase #3 $153.67   12.321%   $172.6037   $172.60   $172.60   $172.60  
  Purchase #4 $240.49   4.321%   $250.8816   $250.88   $250.90   $250.90  
  Purchase #5 $94.96   9.874%   $104.3364   $104.34   $104.35   $104.30  
  Purchase #6 $84.50   10.526%   $93.3945   $93.39   $93.40   $93.40  
  Purchase #7 $171.86   8.803%   $186.9888   $186.99   $187.00   $187.00  
  7 purchase totals = $1,140.94       $1,239.1843   $1,239.18   $1,239.25   $1,239.20