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 $34.77   3.181%   $35.876   $35.88   $35.90   $35.90  
  Purchase #2 $84.71   10.174%   $93.3284   $93.33   $93.35   $93.30  
  Purchase #3 $192.75   4.512%   $201.4469   $201.45   $201.45   $201.40  
  Purchase #4 $172.32   10.379%   $190.2051   $190.21   $190.20   $190.20  
  Purchase #5 $48.87   7.453%   $52.5123   $52.51   $52.50   $52.50  
  Purchase #6 $54.29   5.637%   $57.3503   $57.35   $57.35   $57.40  
  Purchase #7 $58.25   10.311%   $64.2562   $64.26   $64.25   $64.30  
  7 purchase totals = $645.96       $694.9752   $694.99   $695.00   $695.00