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 $17.71   10.821%   $19.6264   $19.63   $19.65   $19.60  
  Purchase #2 $194.74   5.782%   $205.9999   $206.00   $206.00   $206.00  
  Purchase #3 $39.76   3.391%   $41.1083   $41.11   $41.10   $41.10  
  Purchase #4 $169.61   5.469%   $178.886   $178.89   $178.90   $178.90  
  Purchase #5 $27.59   5.862%   $29.2073   $29.21   $29.20   $29.20  
  Purchase #6 $75.83   3.496%   $78.481   $78.48   $78.50   $78.50  
  Purchase #7 $169.82   5.209%   $178.6659   $178.67   $178.65   $178.70  
  7 purchase totals = $695.06       $731.9748   $731.99   $732.00   $732.00