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 $215.67   11.204%   $239.8337   $239.83   $239.85   $239.80  
  Purchase #2 $238.51   7.170%   $255.6112   $255.61   $255.60   $255.60  
  Purchase #3 $92.99   6.423%   $98.9627   $98.96   $98.95   $99.00  
  Purchase #4 $21.70   12.152%   $24.337   $24.34   $24.35   $24.30  
  Purchase #5 $68.27   11.690%   $76.2508   $76.25   $76.25   $76.30  
  Purchase #6 $145.75   6.341%   $154.992   $154.99   $155.00   $155.00  
  Purchase #7 $179.58   3.855%   $186.5028   $186.50   $186.50   $186.50  
  7 purchase totals = $962.47       $1,036.4902   $1,036.48   $1,036.50   $1,036.50