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 $241.90   9.233%   $264.2346   $264.23   $264.25   $264.20  
  Purchase #2 $209.52   11.378%   $233.3592   $233.36   $233.35   $233.40  
  Purchase #3 $100.33   11.451%   $111.8188   $111.82   $111.80   $111.80  
  Purchase #4 $200.94   3.851%   $208.6782   $208.68   $208.70   $208.70  
  Purchase #5 $8.26   11.735%   $9.2293   $9.23   $9.25   $9.20  
  Purchase #6 $161.58   13.719%   $183.7472   $183.75   $183.75   $183.70  
  Purchase #7 $182.80   9.361%   $199.9119   $199.91   $199.90   $199.90  
  7 purchase totals = $1,105.33       $1,210.9792   $1,210.98   $1,211.00   $1,210.90