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 $243.90   6.835%   $260.5706   $260.57   $260.55   $260.60  
  Purchase #2 $223.83   13.115%   $253.1853   $253.19   $253.20   $253.20  
  Purchase #3 $65.96   11.298%   $73.4122   $73.41   $73.40   $73.40  
  Purchase #4 $164.92   13.292%   $186.8412   $186.84   $186.85   $186.80  
  Purchase #5 $218.36   6.667%   $232.9181   $232.92   $232.90   $232.90  
  Purchase #6 $178.60   3.827%   $185.435   $185.44   $185.45   $185.40  
  Purchase #7 $89.73   5.284%   $94.4713   $94.47   $94.45   $94.50  
  7 purchase totals = $1,185.30       $1,286.8337   $1,286.84   $1,286.80   $1,286.80