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 $247.67   11.184%   $275.3694   $275.37   $275.35   $275.40  
  Purchase #2 $166.69   4.720%   $174.5578   $174.56   $174.55   $174.60  
  Purchase #3 $76.54   4.279%   $79.8151   $79.82   $79.80   $79.80  
  Purchase #4 $226.44   9.103%   $247.0528   $247.05   $247.05   $247.10  
  Purchase #5 $97.41   6.183%   $103.4329   $103.43   $103.45   $103.40  
  Purchase #6 $105.36   9.757%   $115.64   $115.64   $115.65   $115.60  
  Purchase #7 $125.69   11.541%   $140.1959   $140.20   $140.20   $140.20  
  7 purchase totals = $1,045.80       $1,136.0639   $1,136.07   $1,136.05   $1,136.10