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 $189.33   13.745%   $215.3534   $215.35   $215.35   $215.40  
  Purchase #2 $216.65   10.160%   $238.6616   $238.66   $238.65   $238.70  
  Purchase #3 $62.73   7.156%   $67.219   $67.22   $67.20   $67.20  
  Purchase #4 $167.32   13.382%   $189.7108   $189.71   $189.70   $189.70  
  Purchase #5 $171.40   7.466%   $184.1967   $184.20   $184.20   $184.20  
  Purchase #6 $14.56   4.821%   $15.2619   $15.26   $15.25   $15.30  
  Purchase #7 $194.67   7.571%   $209.4085   $209.41   $209.40   $209.40  
  7 purchase totals = $1,016.66       $1,119.8119   $1,119.81   $1,119.75   $1,119.90