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	$177.49	6.539%	$189.0961	$189.10	$189.10	$189.10
Purchase #2	$85.42	5.481%	$90.1019	$90.10	$90.10	$90.10
Purchase #3	$64.60	13.283%	$73.1808	$73.18	$73.20	$73.20
Purchase #4	$100.32	9.198%	$109.5474	$109.55	$109.55	$109.50
Purchase #5	$231.36	13.538%	$262.6815	$262.68	$262.70	$262.70
Purchase #6	$110.51	9.161%	$120.6338	$120.63	$120.65	$120.60
Purchase #7	$172.98	13.844%	$196.9274	$196.93	$196.95	$196.90
7 purchase totals =	$942.68		$1,042.1689	$1,042.17	$1,042.25	$1,042.10