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	$75.78	5.860%	$80.2207	$80.22	$80.20	$80.20
Purchase #2	$62.76	12.788%	$70.7857	$70.79	$70.80	$70.80
Purchase #3	$78.42	3.172%	$80.9075	$80.91	$80.90	$80.90
Purchase #4	$37.66	13.828%	$42.8676	$42.87	$42.85	$42.90
Purchase #5	$75.41	3.288%	$77.8895	$77.89	$77.90	$77.90
Purchase #6	$141.77	12.612%	$159.65	$159.65	$159.65	$159.70
Purchase #7	$45.27	7.165%	$48.5136	$48.51	$48.50	$48.50
7 purchase totals =	$517.07		$560.8346	$560.84	$560.80	$560.90