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 $190.85   11.618%   $213.023   $213.02   $213.00   $213.00  
  Purchase #2 $83.87   10.200%   $92.4247   $92.42   $92.40   $92.40  
  Purchase #3 $248.63   3.450%   $257.2077   $257.21   $257.20   $257.20  
  Purchase #4 $85.41   6.462%   $90.9292   $90.93   $90.95   $90.90  
  Purchase #5 $210.68   7.154%   $225.752   $225.75   $225.75   $225.80  
  Purchase #6 $47.77   5.295%   $50.2994   $50.30   $50.30   $50.30  
  Purchase #7 $162.88   5.143%   $171.2569   $171.26   $171.25   $171.30  
  7 purchase totals = $1,030.09       $1,100.8929   $1,100.89   $1,100.85   $1,100.90