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 $197.46   13.567%   $224.2494   $224.25   $224.25   $224.20  
  Purchase #2 $11.27   5.113%   $11.8462   $11.85   $11.85   $11.80  
  Purchase #3 $95.44   3.512%   $98.7919   $98.79   $98.80   $98.80  
  Purchase #4 $208.34   3.264%   $215.1402   $215.14   $215.15   $215.10  
  Purchase #5 $166.89   10.640%   $184.6471   $184.65   $184.65   $184.60  
  Purchase #6 $93.46   9.311%   $102.1621   $102.16   $102.15   $102.20  
  Purchase #7 $182.77   6.744%   $195.096   $195.10   $195.10   $195.10  
  7 purchase totals = $955.63       $1,031.9329   $1,031.94   $1,031.95   $1,031.80