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 $62.29   10.462%   $68.8068   $68.81   $68.80   $68.80  
  Purchase #2 $233.87   4.849%   $245.2104   $245.21   $245.20   $245.20  
  Purchase #3 $16.75   9.608%   $18.3593   $18.36   $18.35   $18.40  
  Purchase #4 $188.60   13.513%   $214.0855   $214.09   $214.10   $214.10  
  Purchase #5 $185.95   9.397%   $203.4237   $203.42   $203.40   $203.40  
  Purchase #6 $194.56   4.572%   $203.4553   $203.46   $203.45   $203.50  
  Purchase #7 $57.44   3.651%   $59.5371   $59.54   $59.55   $59.50  
  7 purchase totals = $939.46       $1,012.8781   $1,012.89   $1,012.85   $1,012.90