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	$236.54	13.628%	$268.7757	$268.78	$268.80	$268.80
Purchase #2	$165.79	6.515%	$176.5912	$176.59	$176.60	$176.60
Purchase #3	$36.64	11.310%	$40.784	$40.78	$40.80	$40.80
Purchase #4	$66.40	8.339%	$71.9371	$71.94	$71.95	$71.90
Purchase #5	$223.70	13.661%	$254.2597	$254.26	$254.25	$254.30
Purchase #6	$88.31	9.197%	$96.4319	$96.43	$96.45	$96.40
Purchase #7	$172.99	9.624%	$189.6386	$189.64	$189.65	$189.60
7 purchase totals =	$990.37		$1,098.4182	$1,098.42	$1,098.50	$1,098.40