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 $56.94   3.450%   $58.9044   $58.90   $58.90   $58.90  
  Purchase #2 $245.87   12.619%   $276.8963   $276.90   $276.90   $276.90  
  Purchase #3 $194.63   11.631%   $217.2674   $217.27   $217.25   $217.30  
  Purchase #4 $169.31   9.273%   $185.0101   $185.01   $185.00   $185.00  
  Purchase #5 $168.66   4.380%   $176.0473   $176.05   $176.05   $176.00  
  Purchase #6 $223.83   9.165%   $244.344   $244.34   $244.35   $244.30  
  Purchase #7 $221.74   3.292%   $229.0397   $229.04   $229.05   $229.00  
  7 purchase totals = $1,280.98       $1,387.5092   $1,387.51   $1,387.50   $1,387.40