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 $29.65   13.268%   $33.584   $33.58   $33.60   $33.60  
  Purchase #2 $149.58   13.493%   $169.7628   $169.76   $169.75   $169.80  
  Purchase #3 $119.40   6.176%   $126.7741   $126.77   $126.75   $126.80  
  Purchase #4 $168.47   7.615%   $181.299   $181.30   $181.30   $181.30  
  Purchase #5 $95.70   12.113%   $107.2921   $107.29   $107.30   $107.30  
  Purchase #6 $60.64   10.346%   $66.9138   $66.91   $66.90   $66.90  
  Purchase #7 $207.41   5.317%   $218.438   $218.44   $218.45   $218.40  
  7 purchase totals = $830.85       $904.0638   $904.05   $904.05   $904.10