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 $60.25   9.702%   $66.0955   $66.10   $66.10   $66.10  
  Purchase #2 $232.44   3.761%   $241.1821   $241.18   $241.20   $241.20  
  Purchase #3 $76.60   10.724%   $84.8146   $84.81   $84.80   $84.80  
  Purchase #4 $10.97   13.551%   $12.4565   $12.46   $12.45   $12.50  
  Purchase #5 $166.53   9.511%   $182.3687   $182.37   $182.35   $182.40  
  Purchase #6 $82.89   8.450%   $89.8942   $89.89   $89.90   $89.90  
  Purchase #7 $77.70   13.586%   $88.2563   $88.26   $88.25   $88.30  
  7 purchase totals = $707.38       $765.0679   $765.07   $765.05   $765.20