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 $62.58   6.712%   $66.7804   $66.78   $66.80   $66.80  
  Purchase #2 $200.33   3.479%   $207.2995   $207.30   $207.30   $207.30  
  Purchase #3 $49.44   7.440%   $53.1183   $53.12   $53.10   $53.10  
  Purchase #4 $137.41   3.607%   $142.3664   $142.37   $142.35   $142.40  
  Purchase #5 $60.38   11.310%   $67.209   $67.21   $67.20   $67.20  
  Purchase #6 $219.49   13.291%   $248.6624   $248.66   $248.65   $248.70  
  Purchase #7 $96.37   13.493%   $109.3732   $109.37   $109.35   $109.40  
  7 purchase totals = $826.00       $894.8092   $894.81   $894.75   $894.90