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 $61.55   11.706%   $68.755   $68.76   $68.75   $68.80  
  Purchase #2 $208.33   4.577%   $217.8653   $217.87   $217.85   $217.90  
  Purchase #3 $71.95   9.573%   $78.8378   $78.84   $78.85   $78.80  
  Purchase #4 $243.29   13.474%   $276.0709   $276.07   $276.05   $276.10  
  Purchase #5 $45.29   13.285%   $51.3068   $51.31   $51.30   $51.30  
  Purchase #6 $103.45   13.495%   $117.4106   $117.41   $117.40   $117.40  
  Purchase #7 $107.87   6.600%   $114.9894   $114.99   $115.00   $115.00  
  7 purchase totals = $841.73       $925.2358   $925.25   $925.20   $925.30