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	$56.54	5.322%	$59.5491	$59.55	$59.55	$59.50
Purchase #2	$222.61	3.546%	$230.5038	$230.50	$230.50	$230.50
Purchase #3	$210.85	13.345%	$238.9879	$238.99	$239.00	$239.00
Purchase #4	$142.85	4.194%	$148.8411	$148.84	$148.85	$148.80
Purchase #5	$138.44	10.339%	$152.7533	$152.75	$152.75	$152.80
Purchase #6	$142.74	11.767%	$159.5362	$159.54	$159.55	$159.50
Purchase #7	$168.42	12.623%	$189.6797	$189.68	$189.70	$189.70
7 purchase totals =	$1,082.45		$1,179.8511	$1,179.85	$1,179.90	$1,179.80