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 $200.27   3.285%   $206.8489   $206.85   $206.85   $206.80  
  Purchase #2 $243.66   9.576%   $266.9929   $266.99   $267.00   $267.00  
  Purchase #3 $45.71   12.133%   $51.256   $51.26   $51.25   $51.30  
  Purchase #4 $224.81   6.513%   $239.4519   $239.45   $239.45   $239.50  
  Purchase #5 $189.70   6.519%   $202.0665   $202.07   $202.05   $202.10  
  Purchase #6 $68.49   11.248%   $76.1938   $76.19   $76.20   $76.20  
  Purchase #7 $241.25   9.267%   $263.6066   $263.61   $263.60   $263.60  
  7 purchase totals = $1,213.89       $1,306.4166   $1,306.42   $1,306.40   $1,306.50