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 $106.66   10.787%   $118.1654   $118.17   $118.15   $118.20  
  Purchase #2 $176.53   10.239%   $194.6049   $194.60   $194.60   $194.60  
  Purchase #3 $16.86   8.817%   $18.3465   $18.35   $18.35   $18.30  
  Purchase #4 $118.32   3.332%   $122.2624   $122.26   $122.25   $122.30  
  Purchase #5 $246.50   3.509%   $255.1497   $255.15   $255.15   $255.10  
  Purchase #6 $202.27   3.650%   $209.6529   $209.65   $209.65   $209.70  
  Purchase #7 $239.97   11.312%   $267.1154   $267.12   $267.10   $267.10  
  7 purchase totals = $1,107.11       $1,185.2972   $1,185.30   $1,185.25   $1,185.30