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	$42.72	11.683%	$47.711	$47.71	$47.70	$47.70
Purchase #2	$115.41	10.390%	$127.4011	$127.40	$127.40	$127.40
Purchase #3	$129.39	5.555%	$136.5776	$136.58	$136.60	$136.60
Purchase #4	$237.93	11.317%	$264.8565	$264.86	$264.85	$264.90
Purchase #5	$231.73	11.782%	$259.0324	$259.03	$259.05	$259.00
Purchase #6	$117.69	13.479%	$133.5534	$133.55	$133.55	$133.60
Purchase #7	$204.59	3.400%	$211.5461	$211.55	$211.55	$211.50
7 purchase totals =	$1,079.46		$1,180.6781	$1,180.68	$1,180.70	$1,180.70