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	$59.48	3.245%	$61.4101	$61.41	$61.40	$61.40
Purchase #2	$140.40	4.604%	$146.864	$146.86	$146.85	$146.90
Purchase #3	$53.64	3.506%	$55.5206	$55.52	$55.50	$55.50
Purchase #4	$67.81	7.234%	$72.7154	$72.72	$72.70	$72.70
Purchase #5	$45.43	7.309%	$48.7505	$48.75	$48.75	$48.80
Purchase #6	$136.69	4.853%	$143.3236	$143.32	$143.30	$143.30
Purchase #7	$11.54	3.308%	$11.9217	$11.92	$11.90	$11.90
7 purchase totals =	$514.99		$540.5059	$540.50	$540.40	$540.50