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 $68.92   5.859%   $72.958   $72.96   $72.95   $73.00  
  Purchase #2 $94.28   7.169%   $101.0389   $101.04   $101.05   $101.00  
  Purchase #3 $158.38   9.614%   $173.6067   $173.61   $173.60   $173.60  
  Purchase #4 $78.82   8.471%   $85.4968   $85.50   $85.50   $85.50  
  Purchase #5 $161.37   11.464%   $179.8695   $179.87   $179.85   $179.90  
  Purchase #6 $50.87   12.247%   $57.1   $57.10   $57.10   $57.10  
  Purchase #7 $76.33   6.429%   $81.2373   $81.24   $81.25   $81.20  
  7 purchase totals = $688.97       $751.3072   $751.32   $751.30   $751.30