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	$173.42	9.209%	$189.3902	$189.39	$189.40	$189.40
Purchase #2	$209.70	12.803%	$236.5479	$236.55	$236.55	$236.50
Purchase #3	$211.72	11.125%	$235.2739	$235.27	$235.25	$235.30
Purchase #4	$81.95	10.608%	$90.6433	$90.64	$90.65	$90.60
Purchase #5	$86.79	3.377%	$89.7209	$89.72	$89.70	$89.70
Purchase #6	$125.72	3.825%	$130.5288	$130.53	$130.55	$130.50
Purchase #7	$185.99	12.156%	$208.5989	$208.60	$208.60	$208.60
7 purchase totals =	$1,075.29		$1,180.7039	$1,180.70	$1,180.70	$1,180.60