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	$31.34	7.337%	$33.6394	$33.64	$33.65	$33.60
Purchase #2	$201.70	9.855%	$221.5775	$221.58	$221.60	$221.60
Purchase #3	$44.84	8.756%	$48.7662	$48.77	$48.75	$48.80
Purchase #4	$54.27	9.485%	$59.4175	$59.42	$59.40	$59.40
Purchase #5	$100.73	10.477%	$111.2835	$111.28	$111.30	$111.30
Purchase #6	$169.55	7.727%	$182.6511	$182.65	$182.65	$182.70
Purchase #7	$83.33	8.492%	$90.4064	$90.41	$90.40	$90.40
7 purchase totals =	$685.76		$747.7416	$747.75	$747.75	$747.80