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	$122.88	4.287%	$128.1479	$128.15	$128.15	$128.10
Purchase #2	$138.47	4.172%	$144.247	$144.25	$144.25	$144.20
Purchase #3	$83.35	3.354%	$86.1456	$86.15	$86.15	$86.10
Purchase #4	$158.43	12.873%	$178.8247	$178.82	$178.80	$178.80
Purchase #5	$187.98	7.637%	$202.336	$202.34	$202.35	$202.30
Purchase #6	$136.96	13.491%	$155.4373	$155.44	$155.45	$155.40
Purchase #7	$131.31	10.152%	$144.6406	$144.64	$144.65	$144.60
7 purchase totals =	$959.38		$1,039.7791	$1,039.79	$1,039.80	$1,039.50