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 $85.35   13.704%   $97.0464   $97.05   $97.05   $97.00  
  Purchase #2 $168.71   8.363%   $182.8192   $182.82   $182.80   $182.80  
  Purchase #3 $214.90   9.169%   $234.6042   $234.60   $234.60   $234.60  
  Purchase #4 $140.81   11.542%   $157.0623   $157.06   $157.05   $157.10  
  Purchase #5 $176.94   4.210%   $184.3892   $184.39   $184.40   $184.40  
  Purchase #6 $76.47   3.584%   $79.2107   $79.21   $79.20   $79.20  
  Purchase #7 $91.94   9.294%   $100.4849   $100.48   $100.50   $100.50  
  7 purchase totals = $955.12       $1,035.6169   $1,035.61   $1,035.60   $1,035.60