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	$20.51	8.387%	$22.2302	$22.23	$22.25	$22.20
Purchase #2	$80.65	5.386%	$84.9938	$84.99	$85.00	$85.00
Purchase #3	$19.74	3.819%	$20.4939	$20.49	$20.50	$20.50
Purchase #4	$225.56	10.466%	$249.1671	$249.17	$249.15	$249.20
Purchase #5	$179.66	6.160%	$190.7271	$190.73	$190.75	$190.70
Purchase #6	$200.60	11.269%	$223.2056	$223.21	$223.20	$223.20
Purchase #7	$173.47	13.300%	$196.5415	$196.54	$196.55	$196.50
7 purchase totals =	$900.19		$987.3592	$987.36	$987.40	$987.30