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 $247.69   11.833%   $276.9992   $277.00   $277.00   $277.00  
  Purchase #2 $57.98   5.617%   $61.2367   $61.24   $61.25   $61.20  
  Purchase #3 $108.26   3.272%   $111.8023   $111.80   $111.80   $111.80  
  Purchase #4 $174.78   10.628%   $193.3556   $193.36   $193.35   $193.40  
  Purchase #5 $168.43   12.575%   $189.6101   $189.61   $189.60   $189.60  
  Purchase #6 $243.95   11.652%   $272.3751   $272.38   $272.40   $272.40  
  Purchase #7 $114.35   4.859%   $119.9063   $119.91   $119.90   $119.90  
  7 purchase totals = $1,115.44       $1,225.2853   $1,225.30   $1,225.30   $1,225.30