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 $68.27   9.560%   $74.7966   $74.80   $74.80   $74.80  
  Purchase #2 $14.37   8.339%   $15.5683   $15.57   $15.55   $15.60  
  Purchase #3 $234.28   12.342%   $263.1948   $263.19   $263.20   $263.20  
  Purchase #4 $189.66   5.858%   $200.7703   $200.77   $200.75   $200.80  
  Purchase #5 $71.35   11.686%   $79.688   $79.69   $79.70   $79.70  
  Purchase #6 $199.80   3.419%   $206.6312   $206.63   $206.65   $206.60  
  Purchase #7 $208.34   11.302%   $231.8866   $231.89   $231.90   $231.90  
  7 purchase totals = $986.07       $1,072.5358   $1,072.54   $1,072.55   $1,072.60