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	$25.63	7.481%	$27.5474	$27.55	$27.55	$27.50
Purchase #2	$118.26	12.658%	$133.2294	$133.23	$133.25	$133.20
Purchase #3	$184.57	6.506%	$196.5781	$196.58	$196.60	$196.60
Purchase #4	$106.98	5.550%	$112.9174	$112.92	$112.90	$112.90
Purchase #5	$63.42	12.166%	$71.1357	$71.14	$71.15	$71.10
Purchase #6	$173.63	11.406%	$193.4342	$193.43	$193.45	$193.40
Purchase #7	$41.25	3.662%	$42.7606	$42.76	$42.75	$42.80
7 purchase totals =	$713.74		$777.6028	$777.61	$777.65	$777.50