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 $219.32   13.173%   $248.211   $248.21   $248.20   $248.20  
  Purchase #2 $17.55   9.760%   $19.2629   $19.26   $19.25   $19.30  
  Purchase #3 $186.58   11.466%   $207.9733   $207.97   $207.95   $208.00  
  Purchase #4 $183.92   11.463%   $205.0027   $205.00   $205.00   $205.00  
  Purchase #5 $86.91   11.191%   $96.6361   $96.64   $96.65   $96.60  
  Purchase #6 $229.87   10.457%   $253.9075   $253.91   $253.90   $253.90  
  Purchase #7 $246.27   8.642%   $267.5527   $267.55   $267.55   $267.60  
  7 purchase totals = $1,170.42       $1,298.5462   $1,298.54   $1,298.50   $1,298.60