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 $227.94   8.634%   $247.6203   $247.62   $247.60   $247.60  
  Purchase #2 $42.72   4.795%   $44.7684   $44.77   $44.75   $44.80  
  Purchase #3 $15.41   4.216%   $16.0597   $16.06   $16.05   $16.10  
  Purchase #4 $194.26   11.306%   $216.223   $216.22   $216.20   $216.20  
  Purchase #5 $119.69   11.755%   $133.7596   $133.76   $133.75   $133.80  
  Purchase #6 $248.81   7.187%   $266.692   $266.69   $266.70   $266.70  
  Purchase #7 $169.61   6.791%   $181.1282   $181.13   $181.15   $181.10  
  7 purchase totals = $1,018.44       $1,106.2512   $1,106.25   $1,106.20   $1,106.30