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 $183.70   13.178%   $207.908   $207.91   $207.90   $207.90  
  Purchase #2 $7.49   7.462%   $8.0489   $8.05   $8.05   $8.00  
  Purchase #3 $48.76   6.133%   $51.7505   $51.75   $51.75   $51.80  
  Purchase #4 $99.42   5.749%   $105.1357   $105.14   $105.15   $105.10  
  Purchase #5 $236.94   5.812%   $250.711   $250.71   $250.70   $250.70  
  Purchase #6 $211.45   6.191%   $224.5409   $224.54   $224.55   $224.50  
  Purchase #7 $204.90   6.829%   $218.8926   $218.89   $218.90   $218.90  
  7 purchase totals = $992.66       $1,066.9876   $1,066.99   $1,067.00   $1,066.90