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 $104.78   13.164%   $118.5732   $118.57   $118.55   $118.60  
  Purchase #2 $16.62   6.523%   $17.7041   $17.70   $17.70   $17.70  
  Purchase #3 $187.63   8.281%   $203.1676   $203.17   $203.15   $203.20  
  Purchase #4 $67.41   10.174%   $74.2683   $74.27   $74.25   $74.30  
  Purchase #5 $81.25   6.341%   $86.4021   $86.40   $86.40   $86.40  
  Purchase #6 $139.25   9.388%   $152.3228   $152.32   $152.30   $152.30  
  Purchase #7 $248.48   6.178%   $263.8311   $263.83   $263.85   $263.80  
  7 purchase totals = $845.42       $916.2692   $916.26   $916.20   $916.30