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 $70.91   11.449%   $79.0285   $79.03   $79.05   $79.00  
  Purchase #2 $152.26   5.869%   $161.1961   $161.20   $161.20   $161.20  
  Purchase #3 $206.32   11.299%   $229.6321   $229.63   $229.65   $229.60  
  Purchase #4 $196.53   10.591%   $217.3445   $217.34   $217.35   $217.30  
  Purchase #5 $206.78   9.778%   $226.9989   $227.00   $227.00   $227.00  
  Purchase #6 $116.90   12.278%   $131.253   $131.25   $131.25   $131.30  
  Purchase #7 $146.87   7.291%   $157.5783   $157.58   $157.60   $157.60  
  7 purchase totals = $1,096.57       $1,203.0314   $1,203.03   $1,203.10   $1,203.00