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 $88.81   4.801%   $93.0738   $93.07   $93.05   $93.10  
  Purchase #2 $98.37   6.572%   $104.8349   $104.83   $104.85   $104.80  
  Purchase #3 $229.66   4.442%   $239.8615   $239.86   $239.85   $239.90  
  Purchase #4 $189.75   9.343%   $207.4783   $207.48   $207.50   $207.50  
  Purchase #5 $250.29   4.534%   $261.6381   $261.64   $261.65   $261.60  
  Purchase #6 $232.27   5.597%   $245.2702   $245.27   $245.25   $245.30  
  Purchase #7 $173.53   3.185%   $179.0569   $179.06   $179.05   $179.10  
  7 purchase totals = $1,262.68       $1,331.2137   $1,331.21   $1,331.20   $1,331.30