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 $247.63   7.748%   $266.8164   $266.82   $266.80   $266.80  
  Purchase #2 $157.97   5.725%   $167.0138   $167.01   $167.00   $167.00  
  Purchase #3 $180.85   4.411%   $188.8273   $188.83   $188.85   $188.80  
  Purchase #4 $41.30   8.600%   $44.8518   $44.85   $44.85   $44.90  
  Purchase #5 $157.80   6.808%   $168.543   $168.54   $168.55   $168.50  
  Purchase #6 $228.60   11.366%   $254.5827   $254.58   $254.60   $254.60  
  Purchase #7 $221.41   13.445%   $251.1786   $251.18   $251.20   $251.20  
  7 purchase totals = $1,235.56       $1,341.8136   $1,341.81   $1,341.85   $1,341.80