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 $69.33   11.349%   $77.1983   $77.20   $77.20   $77.20  
  Purchase #2 $54.25   9.561%   $59.4368   $59.44   $59.45   $59.40  
  Purchase #3 $247.93   5.856%   $262.4488   $262.45   $262.45   $262.40  
  Purchase #4 $16.93   3.757%   $17.5661   $17.57   $17.55   $17.60  
  Purchase #5 $162.43   11.677%   $181.397   $181.40   $181.40   $181.40  
  Purchase #6 $181.81   7.516%   $195.4748   $195.47   $195.45   $195.50  
  Purchase #7 $204.55   3.597%   $211.9077   $211.91   $211.90   $211.90  
  7 purchase totals = $937.23       $1,005.4295   $1,005.44   $1,005.40   $1,005.40