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 $91.68   6.768%   $97.8849   $97.88   $97.90   $97.90  
  Purchase #2 $199.97   4.336%   $208.6407   $208.64   $208.65   $208.60  
  Purchase #3 $159.50   5.764%   $168.6936   $168.69   $168.70   $168.70  
  Purchase #4 $131.64   3.206%   $135.8604   $135.86   $135.85   $135.90  
  Purchase #5 $76.77   4.733%   $80.4035   $80.40   $80.40   $80.40  
  Purchase #6 $7.45   6.123%   $7.9062   $7.91   $7.90   $7.90  
  Purchase #7 $205.70   4.368%   $214.685   $214.69   $214.70   $214.70  
  7 purchase totals = $872.71       $914.0743   $914.07   $914.10   $914.10