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 $87.53   11.156%   $97.2948   $97.29   $97.30   $97.30  
  Purchase #2 $70.95   7.631%   $76.3642   $76.36   $76.35   $76.40  
  Purchase #3 $224.53   13.506%   $254.855   $254.86   $254.85   $254.90  
  Purchase #4 $173.92   8.369%   $188.4754   $188.48   $188.50   $188.50  
  Purchase #5 $118.50   3.649%   $122.8241   $122.82   $122.80   $122.80  
  Purchase #6 $16.33   11.733%   $18.246   $18.25   $18.25   $18.20  
  Purchase #7 $5.68   10.364%   $6.2687   $6.27   $6.25   $6.30  
  7 purchase totals = $697.44       $764.3282   $764.33   $764.30   $764.40