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 $203.79   3.659%   $211.2467   $211.25   $211.25   $211.20  
  Purchase #2 $18.86   7.253%   $20.2279   $20.23   $20.25   $20.20  
  Purchase #3 $197.68   5.272%   $208.1017   $208.10   $208.10   $208.10  
  Purchase #4 $233.95   4.225%   $243.8344   $243.83   $243.85   $243.80  
  Purchase #5 $245.75   5.333%   $258.8558   $258.86   $258.85   $258.90  
  Purchase #6 $206.36   4.854%   $216.3767   $216.38   $216.40   $216.40  
  Purchase #7 $153.65   8.128%   $166.1387   $166.14   $166.15   $166.10  
  7 purchase totals = $1,260.04       $1,324.7819   $1,324.79   $1,324.85   $1,324.70