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 $183.75   13.213%   $208.0289   $208.03   $208.05   $208.00  
  Purchase #2 $14.97   11.333%   $16.6666   $16.67   $16.65   $16.70  
  Purchase #3 $155.54   9.694%   $170.618   $170.62   $170.60   $170.60  
  Purchase #4 $245.57   12.335%   $275.8611   $275.86   $275.85   $275.90  
  Purchase #5 $47.51   10.393%   $52.4477   $52.45   $52.45   $52.40  
  Purchase #6 $49.44   5.233%   $52.0272   $52.03   $52.05   $52.00  
  Purchase #7 $88.74   10.457%   $98.0195   $98.02   $98.00   $98.00  
  7 purchase totals = $785.52       $873.6690   $873.68   $873.65   $873.60