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 $76.62   7.213%   $82.1466   $82.15   $82.15   $82.10  
  Purchase #2 $168.34   8.603%   $182.8223   $182.82   $182.80   $182.80  
  Purchase #3 $240.81   6.641%   $256.8022   $256.80   $256.80   $256.80  
  Purchase #4 $231.70   7.299%   $248.6118   $248.61   $248.60   $248.60  
  Purchase #5 $249.36   5.586%   $263.2892   $263.29   $263.30   $263.30  
  Purchase #6 $231.98   4.559%   $242.556   $242.56   $242.55   $242.60  
  Purchase #7 $164.57   5.438%   $173.5193   $173.52   $173.50   $173.50  
  7 purchase totals = $1,363.38       $1,449.7474   $1,449.75   $1,449.70   $1,449.70