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	$159.50	13.559%	$181.1266	$181.13	$181.15	$181.10
Purchase #2	$229.69	4.696%	$240.4762	$240.48	$240.50	$240.50
Purchase #3	$160.29	8.825%	$174.4356	$174.44	$174.45	$174.40
Purchase #4	$135.75	13.181%	$153.6432	$153.64	$153.65	$153.60
Purchase #5	$93.49	12.792%	$105.4492	$105.45	$105.45	$105.40
Purchase #6	$43.60	10.839%	$48.3258	$48.33	$48.35	$48.30
Purchase #7	$220.25	13.757%	$250.5498	$250.55	$250.55	$250.50
7 purchase totals =	$1,042.57		$1,154.0064	$1,154.02	$1,154.10	$1,153.80