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 $94.25   10.637%   $104.2754   $104.28   $104.30   $104.30  
  Purchase #2 $180.61   6.390%   $192.151   $192.15   $192.15   $192.20  
  Purchase #3 $248.67   11.282%   $276.7249   $276.72   $276.70   $276.70  
  Purchase #4 $227.86   6.356%   $242.3428   $242.34   $242.35   $242.30  
  Purchase #5 $248.51   7.153%   $266.2859   $266.29   $266.30   $266.30  
  Purchase #6 $131.55   8.189%   $142.3226   $142.32   $142.30   $142.30  
  Purchase #7 $184.85   8.637%   $200.8155   $200.82   $200.80   $200.80  
  7 purchase totals = $1,316.30       $1,424.9181   $1,424.92   $1,424.90   $1,424.90