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 $82.86   12.593%   $93.2946   $93.29   $93.30   $93.30  
  Purchase #2 $215.34   13.176%   $243.7132   $243.71   $243.70   $243.70  
  Purchase #3 $226.52   9.697%   $248.4856   $248.49   $248.50   $248.50  
  Purchase #4 $21.62   11.532%   $24.1132   $24.11   $24.10   $24.10  
  Purchase #5 $163.90   12.827%   $184.9235   $184.92   $184.90   $184.90  
  Purchase #6 $182.45   5.274%   $192.0724   $192.07   $192.05   $192.10  
  Purchase #7 $76.26   13.248%   $86.3629   $86.36   $86.35   $86.40  
  7 purchase totals = $968.95       $1,072.9654   $1,072.95   $1,072.90   $1,073.00