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	$130.42	13.194%	$147.6276	$147.63	$147.65	$147.60
Purchase #2	$221.66	7.721%	$238.7744	$238.77	$238.75	$238.80
Purchase #3	$129.59	3.738%	$134.4341	$134.43	$134.45	$134.40
Purchase #4	$192.77	13.305%	$218.418	$218.42	$218.40	$218.40
Purchase #5	$76.30	3.416%	$78.9064	$78.91	$78.90	$78.90
Purchase #6	$209.64	12.275%	$235.3733	$235.37	$235.35	$235.40
Purchase #7	$242.76	4.849%	$254.5314	$254.53	$254.55	$254.50
7 purchase totals =	$1,203.14		$1,308.0652	$1,308.06	$1,308.05	$1,308.00