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 $242.62   13.461%   $275.2791   $275.28   $275.30   $275.30  
  Purchase #2 $221.58   11.295%   $246.6075   $246.61   $246.60   $246.60  
  Purchase #3 $77.77   3.560%   $80.5386   $80.54   $80.55   $80.50  
  Purchase #4 $45.84   3.534%   $47.46   $47.46   $47.45   $47.50  
  Purchase #5 $222.72   5.643%   $235.2881   $235.29   $235.30   $235.30  
  Purchase #6 $127.64   3.406%   $131.9874   $131.99   $132.00   $132.00  
  Purchase #7 $69.66   9.833%   $76.5097   $76.51   $76.50   $76.50  
  7 purchase totals = $1,007.83       $1,093.6704   $1,093.68   $1,093.70   $1,093.70