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 $114.82   4.212%   $119.6562   $119.66   $119.65   $119.70  
  Purchase #2 $82.72   5.104%   $86.942   $86.94   $86.95   $86.90  
  Purchase #3 $109.96   4.566%   $114.9808   $114.98   $115.00   $115.00  
  Purchase #4 $32.96   9.753%   $36.1746   $36.17   $36.15   $36.20  
  Purchase #5 $6.43   13.240%   $7.2813   $7.28   $7.30   $7.30  
  Purchase #6 $155.30   5.246%   $163.447   $163.45   $163.45   $163.40  
  Purchase #7 $182.36   8.466%   $197.7986   $197.80   $197.80   $197.80  
  7 purchase totals = $684.55       $726.2805   $726.28   $726.30   $726.30