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	$115.35	10.199%	$127.1145	$127.11	$127.10	$127.10
Purchase #2	$169.58	12.341%	$190.5079	$190.51	$190.50	$190.50
Purchase #3	$155.80	10.273%	$171.8053	$171.81	$171.80	$171.80
Purchase #4	$197.99	9.141%	$216.0883	$216.09	$216.10	$216.10
Purchase #5	$244.51	13.483%	$277.4773	$277.48	$277.50	$277.50
Purchase #6	$123.40	13.651%	$140.2453	$140.25	$140.25	$140.20
Purchase #7	$12.49	6.642%	$13.3196	$13.32	$13.30	$13.30
7 purchase totals =	$1,019.12		$1,136.5582	$1,136.57	$1,136.55	$1,136.50