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 $54.59   11.108%   $60.6539   $60.65   $60.65   $60.70  
  Purchase #2 $126.90   12.284%   $142.4884   $142.49   $142.50   $142.50  
  Purchase #3 $154.73   4.358%   $161.4731   $161.47   $161.45   $161.50  
  Purchase #4 $66.69   4.686%   $69.8151   $69.82   $69.80   $69.80  
  Purchase #5 $188.89   11.752%   $211.0884   $211.09   $211.10   $211.10  
  Purchase #6 $132.65   9.230%   $144.8936   $144.89   $144.90   $144.90  
  Purchase #7 $57.57   11.131%   $63.9781   $63.98   $64.00   $64.00  
  7 purchase totals = $782.02       $854.3906   $854.39   $854.40   $854.50