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 $194.96   3.480%   $201.7446   $201.74   $201.75   $201.70  
  Purchase #2 $16.54   10.820%   $18.3296   $18.33   $18.35   $18.30  
  Purchase #3 $84.83   3.389%   $87.7049   $87.70   $87.70   $87.70  
  Purchase #4 $35.47   6.396%   $37.7387   $37.74   $37.75   $37.70  
  Purchase #5 $171.96   11.811%   $192.2702   $192.27   $192.25   $192.30  
  Purchase #6 $154.59   5.651%   $163.3259   $163.33   $163.35   $163.30  
  Purchase #7 $210.76   3.509%   $218.1556   $218.16   $218.15   $218.20  
  7 purchase totals = $869.11       $919.2695   $919.27   $919.30   $919.20