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 $60.82   7.657%   $65.477   $65.48   $65.50   $65.50  
  Purchase #2 $25.76   3.535%   $26.6706   $26.67   $26.65   $26.70  
  Purchase #3 $166.28   10.632%   $183.9589   $183.96   $183.95   $184.00  
  Purchase #4 $173.68   8.325%   $188.1389   $188.14   $188.15   $188.10  
  Purchase #5 $97.75   3.691%   $101.358   $101.36   $101.35   $101.40  
  Purchase #6 $115.33   13.786%   $131.2294   $131.23   $131.25   $131.20  
  Purchase #7 $82.66   10.707%   $91.5104   $91.51   $91.50   $91.50  
  7 purchase totals = $722.28       $788.3432   $788.35   $788.35   $788.40