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	$250.93	6.231%	$266.5654	$266.57	$266.55	$266.60
Purchase #2	$208.62	10.676%	$230.8923	$230.89	$230.90	$230.90
Purchase #3	$47.78	5.154%	$50.2426	$50.24	$50.25	$50.20
Purchase #4	$31.55	7.406%	$33.8866	$33.89	$33.90	$33.90
Purchase #5	$151.35	9.245%	$165.3423	$165.34	$165.35	$165.30
Purchase #6	$148.87	10.409%	$164.3659	$164.37	$164.35	$164.40
Purchase #7	$68.75	3.722%	$71.3089	$71.31	$71.30	$71.30
7 purchase totals =	$907.85		$982.6040	$982.61	$982.60	$982.60