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 $204.72   4.137%   $213.1893   $213.19   $213.20   $213.20  
  Purchase #2 $20.76   5.166%   $21.8325   $21.83   $21.85   $21.80  
  Purchase #3 $62.41   12.124%   $69.9766   $69.98   $70.00   $70.00  
  Purchase #4 $73.32   13.146%   $82.9586   $82.96   $82.95   $83.00  
  Purchase #5 $27.79   10.174%   $30.6174   $30.62   $30.60   $30.60  
  Purchase #6 $244.25   6.339%   $259.733   $259.73   $259.75   $259.70  
  Purchase #7 $156.53   7.576%   $168.3887   $168.39   $168.40   $168.40  
  7 purchase totals = $789.78       $846.6961   $846.70   $846.75   $846.70