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 $38.55   8.782%   $41.9355   $41.94   $41.95   $41.90  
  Purchase #2 $22.69   9.339%   $24.809   $24.81   $24.80   $24.80  
  Purchase #3 $238.64   9.732%   $261.8644   $261.86   $261.85   $261.90  
  Purchase #4 $167.84   6.314%   $178.4374   $178.44   $178.45   $178.40  
  Purchase #5 $233.74   6.483%   $248.8934   $248.89   $248.90   $248.90  
  Purchase #6 $229.34   9.678%   $251.5355   $251.54   $251.55   $251.50  
  Purchase #7 $118.57   6.255%   $125.9866   $125.99   $126.00   $126.00  
  7 purchase totals = $1,049.37       $1,133.4618   $1,133.47   $1,133.50   $1,133.40