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 $245.26   8.759%   $266.7423   $266.74   $266.75   $266.70  
  Purchase #2 $101.48   10.425%   $112.0593   $112.06   $112.05   $112.10  
  Purchase #3 $89.85   12.250%   $100.8566   $100.86   $100.85   $100.90  
  Purchase #4 $192.27   3.341%   $198.6937   $198.69   $198.70   $198.70  
  Purchase #5 $161.98   12.732%   $182.6033   $182.60   $182.60   $182.60  
  Purchase #6 $112.69   11.527%   $125.6798   $125.68   $125.70   $125.70  
  Purchase #7 $78.27   7.339%   $84.0142   $84.01   $84.00   $84.00  
  7 purchase totals = $981.80       $1,070.6492   $1,070.64   $1,070.65   $1,070.70