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	$178.57	12.444%	$200.7913	$200.79	$200.80	$200.80
Purchase #2	$82.31	6.198%	$87.4116	$87.41	$87.40	$87.40
Purchase #3	$93.28	10.773%	$103.3291	$103.33	$103.35	$103.30
Purchase #4	$133.52	9.847%	$146.6677	$146.67	$146.65	$146.70
Purchase #5	$136.78	9.654%	$149.9847	$149.98	$150.00	$150.00
Purchase #6	$214.95	13.744%	$244.4927	$244.49	$244.50	$244.50
Purchase #7	$74.72	12.708%	$84.2154	$84.22	$84.20	$84.20
7 purchase totals =	$914.13		$1,016.8925	$1,016.89	$1,016.90	$1,016.90