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 $185.99   11.860%   $208.0484   $208.05   $208.05   $208.00  
  Purchase #2 $91.34   7.818%   $98.481   $98.48   $98.50   $98.50  
  Purchase #3 $233.82   7.148%   $250.5335   $250.53   $250.55   $250.50  
  Purchase #4 $104.86   4.821%   $109.9153   $109.92   $109.90   $109.90  
  Purchase #5 $239.77   4.712%   $251.068   $251.07   $251.05   $251.10  
  Purchase #6 $76.30   9.324%   $83.4142   $83.41   $83.40   $83.40  
  Purchase #7 $190.80   5.231%   $200.7807   $200.78   $200.80   $200.80  
  7 purchase totals = $1,122.88       $1,202.2411   $1,202.24   $1,202.25   $1,202.20