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 $244.58   6.261%   $259.8932   $259.89   $259.90   $259.90  
  Purchase #2 $91.54   10.838%   $101.4611   $101.46   $101.45   $101.50  
  Purchase #3 $150.36   12.218%   $168.731   $168.73   $168.75   $168.70  
  Purchase #4 $202.61   5.379%   $213.5084   $213.51   $213.50   $213.50  
  Purchase #5 $224.82   5.283%   $236.6972   $236.70   $236.70   $236.70  
  Purchase #6 $127.49   7.282%   $136.7738   $136.77   $136.75   $136.80  
  Purchase #7 $147.43   4.369%   $153.8712   $153.87   $153.85   $153.90  
  7 purchase totals = $1,188.83       $1,270.9359   $1,270.93   $1,270.90   $1,271.00