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 $195.97   5.476%   $206.7013   $206.70   $206.70   $206.70  
  Purchase #2 $92.96   8.282%   $100.6589   $100.66   $100.65   $100.70  
  Purchase #3 $213.74   6.291%   $227.1864   $227.19   $227.20   $227.20  
  Purchase #4 $118.33   13.319%   $134.0904   $134.09   $134.10   $134.10  
  Purchase #5 $34.99   6.135%   $37.1366   $37.14   $37.15   $37.10  
  Purchase #6 $101.61   12.112%   $113.917   $113.92   $113.90   $113.90  
  Purchase #7 $185.30   12.254%   $208.0067   $208.01   $208.00   $208.00  
  7 purchase totals = $942.90       $1,027.6973   $1,027.71   $1,027.70   $1,027.70