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 $250.48   7.248%   $268.6348   $268.63   $268.65   $268.60  
  Purchase #2 $216.57   8.448%   $234.8658   $234.87   $234.85   $234.90  
  Purchase #3 $58.48   9.374%   $63.9619   $63.96   $63.95   $64.00  
  Purchase #4 $168.31   12.820%   $189.8873   $189.89   $189.90   $189.90  
  Purchase #5 $240.56   10.639%   $266.1532   $266.15   $266.15   $266.20  
  Purchase #6 $180.95   3.687%   $187.6216   $187.62   $187.60   $187.60  
  Purchase #7 $105.46   11.454%   $117.5394   $117.54   $117.55   $117.50  
  7 purchase totals = $1,220.81       $1,328.6640   $1,328.66   $1,328.65   $1,328.70