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	$123.56	12.257%	$138.7047	$138.70	$138.70	$138.70
Purchase #2	$76.73	6.255%	$81.5295	$81.53	$81.55	$81.50
Purchase #3	$161.89	11.867%	$181.1015	$181.10	$181.10	$181.10
Purchase #4	$25.54	10.192%	$28.143	$28.14	$28.15	$28.10
Purchase #5	$161.96	13.670%	$184.0999	$184.10	$184.10	$184.10
Purchase #6	$241.91	5.613%	$255.4884	$255.49	$255.50	$255.50
Purchase #7	$128.69	4.398%	$134.3498	$134.35	$134.35	$134.30
7 purchase totals =	$920.28		$1,003.4168	$1,003.41	$1,003.45	$1,003.30