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	$73.39	13.541%	$83.3277	$83.33	$83.35	$83.30
Purchase #2	$226.57	10.571%	$250.5207	$250.52	$250.50	$250.50
Purchase #3	$106.66	8.286%	$115.4978	$115.50	$115.50	$115.50
Purchase #4	$197.32	5.717%	$208.6008	$208.60	$208.60	$208.60
Purchase #5	$245.91	11.361%	$273.8478	$273.85	$273.85	$273.80
Purchase #6	$117.37	8.336%	$127.154	$127.15	$127.15	$127.20
Purchase #7	$102.64	9.565%	$112.4575	$112.46	$112.45	$112.50
7 purchase totals =	$1,069.86		$1,171.4063	$1,171.41	$1,171.40	$1,171.40