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 $55.35   5.872%   $58.6002   $58.60   $58.60   $58.60  
  Purchase #2 $87.45   5.314%   $92.0971   $92.10   $92.10   $92.10  
  Purchase #3 $123.83   6.647%   $132.061   $132.06   $132.05   $132.10  
  Purchase #4 $195.25   6.579%   $208.0955   $208.10   $208.10   $208.10  
  Purchase #5 $108.76   4.783%   $113.962   $113.96   $113.95   $114.00  
  Purchase #6 $48.51   3.698%   $50.3039   $50.30   $50.30   $50.30  
  Purchase #7 $222.58   4.195%   $231.9172   $231.92   $231.90   $231.90  
  7 purchase totals = $841.73       $887.0369   $887.04   $887.00   $887.10