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 $153.64   7.281%   $164.8265   $164.83   $164.85   $164.80  
  Purchase #2 $70.78   7.855%   $76.3398   $76.34   $76.35   $76.30  
  Purchase #3 $9.88   4.193%   $10.2943   $10.29   $10.30   $10.30  
  Purchase #4 $44.88   3.800%   $46.5854   $46.59   $46.60   $46.60  
  Purchase #5 $230.83   7.530%   $248.2115   $248.21   $248.20   $248.20  
  Purchase #6 $45.63   10.147%   $50.2601   $50.26   $50.25   $50.30  
  Purchase #7 $217.27   4.154%   $226.2954   $226.30   $226.30   $226.30  
  7 purchase totals = $772.91       $822.8130   $822.82   $822.85   $822.80