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 $226.28   7.223%   $242.6242   $242.62   $242.60   $242.60  
  Purchase #2 $68.46   4.832%   $71.768   $71.77   $71.75   $71.80  
  Purchase #3 $174.34   6.702%   $186.0243   $186.02   $186.00   $186.00  
  Purchase #4 $115.50   4.798%   $121.0417   $121.04   $121.05   $121.00  
  Purchase #5 $204.33   6.177%   $216.9515   $216.95   $216.95   $217.00  
  Purchase #6 $96.77   8.173%   $104.679   $104.68   $104.70   $104.70  
  Purchase #7 $233.45   11.111%   $259.3886   $259.39   $259.40   $259.40  
  7 purchase totals = $1,119.13       $1,202.4773   $1,202.47   $1,202.45   $1,202.50