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 $235.89   12.208%   $264.6875   $264.69   $264.70   $264.70  
  Purchase #2 $5.42   3.441%   $5.6065   $5.61   $5.60   $5.60  
  Purchase #3 $238.45   7.338%   $255.9475   $255.95   $255.95   $255.90  
  Purchase #4 $214.83   4.299%   $224.0655   $224.07   $224.05   $224.10  
  Purchase #5 $168.91   7.132%   $180.9567   $180.96   $180.95   $181.00  
  Purchase #6 $214.29   8.158%   $231.7718   $231.77   $231.75   $231.80  
  Purchase #7 $53.26   13.396%   $60.3947   $60.39   $60.40   $60.40  
  7 purchase totals = $1,131.05       $1,223.4302   $1,223.44   $1,223.40   $1,223.50