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	$229.30	8.352%	$248.4511	$248.45	$248.45	$248.50
Purchase #2	$73.35	7.128%	$78.5784	$78.58	$78.60	$78.60
Purchase #3	$86.86	4.684%	$90.9285	$90.93	$90.95	$90.90
Purchase #4	$155.51	3.409%	$160.8113	$160.81	$160.80	$160.80
Purchase #5	$136.60	8.275%	$147.9037	$147.90	$147.90	$147.90
Purchase #6	$21.85	7.308%	$23.4468	$23.45	$23.45	$23.40
Purchase #7	$38.40	3.616%	$39.7885	$39.79	$39.80	$39.80
7 purchase totals =	$741.87		$789.9083	$789.91	$789.95	$789.90