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 $52.26   12.181%   $58.6258   $58.63   $58.65   $58.60  
  Purchase #2 $125.55   6.646%   $133.8941   $133.89   $133.90   $133.90  
  Purchase #3 $85.68   9.690%   $93.9824   $93.98   $94.00   $94.00  
  Purchase #4 $205.37   4.235%   $214.0674   $214.07   $214.05   $214.10  
  Purchase #5 $59.74   8.582%   $64.8669   $64.87   $64.85   $64.90  
  Purchase #6 $137.74   5.808%   $145.7399   $145.74   $145.75   $145.70  
  Purchase #7 $179.47   4.209%   $187.0239   $187.02   $187.00   $187.00  
  7 purchase totals = $845.81       $898.2004   $898.20   $898.20   $898.20