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 $212.60   12.242%   $238.6265   $238.63   $238.65   $238.60  
  Purchase #2 $56.71   7.268%   $60.8317   $60.83   $60.85   $60.80  
  Purchase #3 $208.78   11.807%   $233.4307   $233.43   $233.45   $233.40  
  Purchase #4 $176.87   12.124%   $198.3137   $198.31   $198.30   $198.30  
  Purchase #5 $98.25   12.345%   $110.379   $110.38   $110.40   $110.40  
  Purchase #6 $89.90   4.219%   $93.6929   $93.69   $93.70   $93.70  
  Purchase #7 $245.50   11.296%   $273.2317   $273.23   $273.25   $273.20  
  7 purchase totals = $1,088.61       $1,208.5062   $1,208.50   $1,208.60   $1,208.40