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 $242.68   10.330%   $267.7488   $267.75   $267.75   $267.70  
  Purchase #2 $181.39   7.767%   $195.4786   $195.48   $195.50   $195.50  
  Purchase #3 $86.60   11.420%   $96.4897   $96.49   $96.50   $96.50  
  Purchase #4 $131.46   11.816%   $146.9933   $146.99   $147.00   $147.00  
  Purchase #5 $96.28   12.778%   $108.5827   $108.58   $108.60   $108.60  
  Purchase #6 $187.29   6.686%   $199.8122   $199.81   $199.80   $199.80  
  Purchase #7 $228.69   8.591%   $248.3368   $248.34   $248.35   $248.30  
  7 purchase totals = $1,154.39       $1,263.4421   $1,263.44   $1,263.50   $1,263.40