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 $245.79   10.685%   $272.0527   $272.05   $272.05   $272.10  
  Purchase #2 $77.94   8.622%   $84.66   $84.66   $84.65   $84.70  
  Purchase #3 $176.33   5.430%   $185.9047   $185.90   $185.90   $185.90  
  Purchase #4 $147.94   4.610%   $154.76   $154.76   $154.75   $154.80  
  Purchase #5 $172.33   10.838%   $191.0071   $191.01   $191.00   $191.00  
  Purchase #6 $136.70   12.583%   $153.901   $153.90   $153.90   $153.90  
  Purchase #7 $231.97   5.683%   $245.1529   $245.15   $245.15   $245.20  
  7 purchase totals = $1,189.00       $1,287.4384   $1,287.43   $1,287.40   $1,287.60