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	$179.35	8.323%	$194.2773	$194.28	$194.30	$194.30
Purchase #2	$202.73	13.359%	$229.8127	$229.81	$229.80	$229.80
Purchase #3	$36.43	11.542%	$40.6348	$40.63	$40.65	$40.60
Purchase #4	$35.71	12.230%	$40.0773	$40.08	$40.10	$40.10
Purchase #5	$52.29	4.358%	$54.5688	$54.57	$54.55	$54.60
Purchase #6	$100.55	3.841%	$104.4121	$104.41	$104.40	$104.40
Purchase #7	$167.26	12.707%	$188.5137	$188.51	$188.50	$188.50
7 purchase totals =	$774.32		$852.2967	$852.29	$852.30	$852.30