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	$42.30	9.668%	$46.3896	$46.39	$46.40	$46.40
Purchase #2	$79.65	3.679%	$82.5803	$82.58	$82.60	$82.60
Purchase #3	$132.77	10.130%	$146.2196	$146.22	$146.20	$146.20
Purchase #4	$50.66	9.174%	$55.3075	$55.31	$55.30	$55.30
Purchase #5	$159.95	5.682%	$169.0384	$169.04	$169.05	$169.00
Purchase #6	$58.40	7.114%	$62.5546	$62.55	$62.55	$62.60
Purchase #7	$57.99	11.228%	$64.5011	$64.50	$64.50	$64.50
7 purchase totals =	$581.72		$626.5911	$626.59	$626.60	$626.60