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 $192.62   8.361%   $208.725   $208.73   $208.75   $208.70  
  Purchase #2 $200.62   5.593%   $211.8407   $211.84   $211.85   $211.80  
  Purchase #3 $111.70   5.297%   $117.6167   $117.62   $117.60   $117.60  
  Purchase #4 $233.71   6.762%   $249.5135   $249.51   $249.50   $249.50  
  Purchase #5 $188.27   12.606%   $212.0033   $212.00   $212.00   $212.00  
  Purchase #6 $180.37   10.147%   $198.6721   $198.67   $198.65   $198.70  
  Purchase #7 $136.86   8.431%   $148.3987   $148.40   $148.40   $148.40  
  7 purchase totals = $1,244.15       $1,346.7700   $1,346.77   $1,346.75   $1,346.70