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 $199.84   13.716%   $227.2501   $227.25   $227.25   $227.30  
  Purchase #2 $60.74   3.726%   $63.0032   $63.00   $63.00   $63.00  
  Purchase #3 $216.65   4.591%   $226.5964   $226.60   $226.60   $226.60  
  Purchase #4 $174.44   11.307%   $194.1639   $194.16   $194.15   $194.20  
  Purchase #5 $78.74   11.433%   $87.7423   $87.74   $87.75   $87.70  
  Purchase #6 $58.31   9.217%   $63.6844   $63.68   $63.70   $63.70  
  Purchase #7 $9.62   10.848%   $10.6636   $10.66   $10.65   $10.70  
  7 purchase totals = $798.34       $873.1039   $873.09   $873.10   $873.20