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 $244.92   12.678%   $275.971   $275.97   $275.95   $276.00  
  Purchase #2 $174.76   4.679%   $182.937   $182.94   $182.95   $182.90  
  Purchase #3 $50.71   11.577%   $56.5807   $56.58   $56.60   $56.60  
  Purchase #4 $169.88   7.800%   $183.1306   $183.13   $183.15   $183.10  
  Purchase #5 $132.70   3.474%   $137.31   $137.31   $137.30   $137.30  
  Purchase #6 $213.37   11.856%   $238.6671   $238.67   $238.65   $238.70  
  Purchase #7 $83.27   3.403%   $86.1037   $86.10   $86.10   $86.10  
  7 purchase totals = $1,069.61       $1,160.7001   $1,160.70   $1,160.70   $1,160.70