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	$144.63	10.150%	$159.3099	$159.31	$159.30	$159.30
Purchase #2	$90.61	4.280%	$94.4881	$94.49	$94.50	$94.50
Purchase #3	$152.45	3.838%	$158.301	$158.30	$158.30	$158.30
Purchase #4	$149.36	6.264%	$158.7159	$158.72	$158.70	$158.70
Purchase #5	$127.31	3.508%	$131.776	$131.78	$131.80	$131.80
Purchase #6	$210.98	9.658%	$231.3564	$231.36	$231.35	$231.40
Purchase #7	$165.31	6.312%	$175.7444	$175.74	$175.75	$175.70
7 purchase totals =	$1,040.65		$1,109.6917	$1,109.70	$1,109.70	$1,109.70