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 $211.45   11.726%   $236.2446   $236.24   $236.25   $236.20  
  Purchase #2 $108.74   10.699%   $120.3741   $120.37   $120.35   $120.40  
  Purchase #3 $194.96   6.112%   $206.876   $206.88   $206.90   $206.90  
  Purchase #4 $120.78   3.771%   $125.3346   $125.33   $125.35   $125.30  
  Purchase #5 $192.65   6.606%   $205.3765   $205.38   $205.40   $205.40  
  Purchase #6 $224.83   10.735%   $248.9655   $248.97   $248.95   $249.00  
  Purchase #7 $85.81   4.315%   $89.5127   $89.51   $89.50   $89.50  
  7 purchase totals = $1,139.22       $1,232.6840   $1,232.68   $1,232.70   $1,232.70