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 $240.44   11.426%   $267.9127   $267.91   $267.90   $267.90  
  Purchase #2 $137.79   7.602%   $148.2648   $148.26   $148.25   $148.30  
  Purchase #3 $191.39   10.628%   $211.7309   $211.73   $211.75   $211.70  
  Purchase #4 $66.58   5.466%   $70.2193   $70.22   $70.20   $70.20  
  Purchase #5 $186.43   9.499%   $204.139   $204.14   $204.15   $204.10  
  Purchase #6 $23.61   8.265%   $25.5614   $25.56   $25.55   $25.60  
  Purchase #7 $249.33   4.442%   $260.4052   $260.41   $260.40   $260.40  
  7 purchase totals = $1,095.57       $1,188.2333   $1,188.23   $1,188.20   $1,188.20