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 $205.58   7.103%   $220.1823   $220.18   $220.20   $220.20  
  Purchase #2 $151.94   13.437%   $172.3562   $172.36   $172.35   $172.40  
  Purchase #3 $114.37   5.393%   $120.538   $120.54   $120.55   $120.50  
  Purchase #4 $249.76   4.823%   $261.8059   $261.81   $261.80   $261.80  
  Purchase #5 $214.43   5.746%   $226.7511   $226.75   $226.75   $226.80  
  Purchase #6 $205.29   5.674%   $216.9382   $216.94   $216.95   $216.90  
  Purchase #7 $69.95   7.743%   $75.3662   $75.37   $75.35   $75.40  
  7 purchase totals = $1,211.32       $1,293.9379   $1,293.95   $1,293.95   $1,294.00