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 $63.46   11.580%   $70.8087   $70.81   $70.80   $70.80  
  Purchase #2 $51.90   3.677%   $53.8084   $53.81   $53.80   $53.80  
  Purchase #3 $15.93   7.341%   $17.0994   $17.10   $17.10   $17.10  
  Purchase #4 $50.44   10.802%   $55.8885   $55.89   $55.90   $55.90  
  Purchase #5 $233.90   12.587%   $263.341   $263.34   $263.35   $263.30  
  Purchase #6 $163.84   13.333%   $185.6848   $185.68   $185.70   $185.70  
  Purchase #7 $242.50   9.362%   $265.2029   $265.20   $265.20   $265.20  
  7 purchase totals = $821.97       $911.8337   $911.83   $911.85   $911.80