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	$150.95	13.694%	$171.6211	$171.62	$171.60	$171.60
Purchase #2	$105.77	3.534%	$109.5079	$109.51	$109.50	$109.50
Purchase #3	$68.34	9.281%	$74.6826	$74.68	$74.70	$74.70
Purchase #4	$50.34	11.443%	$56.1004	$56.10	$56.10	$56.10
Purchase #5	$216.66	10.129%	$238.6055	$238.61	$238.60	$238.60
Purchase #6	$36.60	13.820%	$41.6581	$41.66	$41.65	$41.70
Purchase #7	$161.56	3.621%	$167.4101	$167.41	$167.40	$167.40
7 purchase totals =	$790.22		$859.5857	$859.59	$859.55	$859.60