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 $245.62   8.687%   $266.957   $266.96   $266.95   $267.00  
  Purchase #2 $135.98   13.468%   $154.2938   $154.29   $154.30   $154.30  
  Purchase #3 $59.48   3.443%   $61.5279   $61.53   $61.55   $61.50  
  Purchase #4 $45.71   8.221%   $49.4678   $49.47   $49.45   $49.50  
  Purchase #5 $109.76   4.478%   $114.6751   $114.68   $114.70   $114.70  
  Purchase #6 $5.76   4.512%   $6.0199   $6.02   $6.00   $6.00  
  Purchase #7 $172.45   7.255%   $184.9612   $184.96   $184.95   $185.00  
  7 purchase totals = $774.76       $837.9027   $837.91   $837.90   $838.00