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	$56.33	5.492%	$59.4236	$59.42	$59.40	$59.40
Purchase #2	$34.61	3.839%	$35.9387	$35.94	$35.95	$35.90
Purchase #3	$136.25	12.851%	$153.7595	$153.76	$153.75	$153.80
Purchase #4	$191.72	11.209%	$213.2099	$213.21	$213.20	$213.20
Purchase #5	$226.56	5.336%	$238.6492	$238.65	$238.65	$238.60
Purchase #6	$154.70	11.627%	$172.687	$172.69	$172.70	$172.70
Purchase #7	$33.35	7.259%	$35.7709	$35.77	$35.75	$35.80
7 purchase totals =	$833.52		$909.4388	$909.44	$909.40	$909.40