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 $162.72   5.872%   $172.2749   $172.27   $172.25   $172.30  
  Purchase #2 $51.51   4.602%   $53.8805   $53.88   $53.90   $53.90  
  Purchase #3 $202.44   12.141%   $227.0182   $227.02   $227.00   $227.00  
  Purchase #4 $161.29   4.386%   $168.3642   $168.36   $168.35   $168.40  
  Purchase #5 $150.36   8.151%   $162.6158   $162.62   $162.60   $162.60  
  Purchase #6 $245.54   11.439%   $273.6273   $273.63   $273.65   $273.60  
  Purchase #7 $61.46   11.777%   $68.6981   $68.70   $68.70   $68.70  
  7 purchase totals = $1,035.32       $1,126.4790   $1,126.48   $1,126.45   $1,126.50