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 $61.32   8.177%   $66.3341   $66.33   $66.35   $66.30  
  Purchase #2 $102.57   9.269%   $112.0772   $112.08   $112.10   $112.10  
  Purchase #3 $232.38   3.572%   $240.6806   $240.68   $240.70   $240.70  
  Purchase #4 $161.77   6.394%   $172.1136   $172.11   $172.10   $172.10  
  Purchase #5 $119.76   11.510%   $133.5444   $133.54   $133.55   $133.50  
  Purchase #6 $160.71   9.171%   $175.4487   $175.45   $175.45   $175.40  
  Purchase #7 $54.68   13.351%   $61.9803   $61.98   $62.00   $62.00  
  7 purchase totals = $893.19       $962.1789   $962.17   $962.25   $962.10