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 $172.65   13.423%   $195.8248   $195.82   $195.80   $195.80  
  Purchase #2 $83.87   9.378%   $91.7353   $91.74   $91.75   $91.70  
  Purchase #3 $95.71   3.217%   $98.789   $98.79   $98.80   $98.80  
  Purchase #4 $207.40   13.122%   $234.615   $234.62   $234.60   $234.60  
  Purchase #5 $131.66   7.699%   $141.7965   $141.80   $141.80   $141.80  
  Purchase #6 $65.50   4.777%   $68.6289   $68.63   $68.65   $68.60  
  Purchase #7 $25.94   8.163%   $28.0575   $28.06   $28.05   $28.10  
  7 purchase totals = $782.73       $859.4470   $859.46   $859.45   $859.40