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 $207.99   3.373%   $215.0055   $215.01   $215.00   $215.00  
  Purchase #2 $168.99   3.503%   $174.9097   $174.91   $174.90   $174.90  
  Purchase #3 $30.98   11.601%   $34.574   $34.57   $34.55   $34.60  
  Purchase #4 $90.73   9.113%   $98.9982   $99.00   $99.00   $99.00  
  Purchase #5 $100.83   5.696%   $106.5733   $106.57   $106.55   $106.60  
  Purchase #6 $215.40   11.328%   $239.8005   $239.80   $239.80   $239.80  
  Purchase #7 $87.49   6.316%   $93.0159   $93.02   $93.00   $93.00  
  7 purchase totals = $902.41       $962.8771   $962.88   $962.80   $962.90