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 $176.90   9.299%   $193.3499   $193.35   $193.35   $193.30  
  Purchase #2 $52.56   12.246%   $58.9965   $59.00   $59.00   $59.00  
  Purchase #3 $81.58   8.364%   $88.4034   $88.40   $88.40   $88.40  
  Purchase #4 $117.47   6.617%   $125.243   $125.24   $125.25   $125.20  
  Purchase #5 $131.67   4.673%   $137.8229   $137.82   $137.80   $137.80  
  Purchase #6 $157.76   13.473%   $179.015   $179.02   $179.00   $179.00  
  Purchase #7 $192.85   12.282%   $216.5358   $216.54   $216.55   $216.50  
  7 purchase totals = $910.79       $999.3665   $999.37   $999.35   $999.20