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 $248.35   11.237%   $276.2571   $276.26   $276.25   $276.30  
  Purchase #2 $23.31   10.867%   $25.8431   $25.84   $25.85   $25.80  
  Purchase #3 $158.58   10.227%   $174.798   $174.80   $174.80   $174.80  
  Purchase #4 $87.45   7.347%   $93.875   $93.88   $93.90   $93.90  
  Purchase #5 $225.35   5.184%   $237.0321   $237.03   $237.05   $237.00  
  Purchase #6 $19.86   10.214%   $21.8885   $21.89   $21.90   $21.90  
  Purchase #7 $41.76   7.441%   $44.8674   $44.87   $44.85   $44.90  
  7 purchase totals = $804.66       $874.5612   $874.57   $874.60   $874.60