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 $188.77   9.646%   $206.9788   $206.98   $207.00   $207.00  
  Purchase #2 $55.50   5.614%   $58.6158   $58.62   $58.60   $58.60  
  Purchase #3 $229.69   10.112%   $252.9163   $252.92   $252.90   $252.90  
  Purchase #4 $124.88   13.119%   $141.263   $141.26   $141.25   $141.30  
  Purchase #5 $38.84   5.452%   $40.9576   $40.96   $40.95   $41.00  
  Purchase #6 $47.62   11.766%   $53.223   $53.22   $53.20   $53.20  
  Purchase #7 $241.83   11.855%   $270.4989   $270.50   $270.50   $270.50  
  7 purchase totals = $927.13       $1,024.4534   $1,024.46   $1,024.40   $1,024.50