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 $76.37   13.788%   $86.8999   $86.90   $86.90   $86.90  
  Purchase #2 $134.92   8.303%   $146.1224   $146.12   $146.10   $146.10  
  Purchase #3 $26.73   7.626%   $28.7684   $28.77   $28.75   $28.80  
  Purchase #4 $86.92   10.699%   $96.2196   $96.22   $96.20   $96.20  
  Purchase #5 $162.30   12.653%   $182.8358   $182.84   $182.85   $182.80  
  Purchase #6 $225.86   8.784%   $245.6995   $245.70   $245.70   $245.70  
  Purchase #7 $225.47   13.671%   $256.294   $256.29   $256.30   $256.30  
  7 purchase totals = $938.57       $1,042.8396   $1,042.84   $1,042.80   $1,042.80