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 $167.69   10.625%   $185.5071   $185.51   $185.50   $185.50  
  Purchase #2 $117.40   4.531%   $122.7194   $122.72   $122.70   $122.70  
  Purchase #3 $82.25   9.502%   $90.0654   $90.07   $90.05   $90.10  
  Purchase #4 $174.63   6.122%   $185.3208   $185.32   $185.30   $185.30  
  Purchase #5 $121.73   11.184%   $135.3443   $135.34   $135.35   $135.30  
  Purchase #6 $111.27   8.671%   $120.9182   $120.92   $120.90   $120.90  
  Purchase #7 $183.40   5.827%   $194.0867   $194.09   $194.10   $194.10  
  7 purchase totals = $958.37       $1,033.9619   $1,033.97   $1,033.90   $1,033.90