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 $48.84   7.691%   $52.5963   $52.60   $52.60   $52.60  
  Purchase #2 $97.50   4.432%   $101.8212   $101.82   $101.80   $101.80  
  Purchase #3 $94.57   3.201%   $97.5972   $97.60   $97.60   $97.60  
  Purchase #4 $77.42   6.518%   $82.4662   $82.47   $82.45   $82.50  
  Purchase #5 $217.97   12.218%   $244.6016   $244.60   $244.60   $244.60  
  Purchase #6 $6.76   4.431%   $7.0595   $7.06   $7.05   $7.10  
  Purchase #7 $178.39   13.183%   $201.9072   $201.91   $201.90   $201.90  
  7 purchase totals = $721.45       $788.0492   $788.06   $788.00   $788.10