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	$244.66	6.873%	$261.4755	$261.48	$261.50	$261.50
Purchase #2	$173.27	3.786%	$179.83	$179.83	$179.85	$179.80
Purchase #3	$49.83	4.385%	$52.015	$52.02	$52.00	$52.00
Purchase #4	$103.79	12.412%	$116.6724	$116.67	$116.65	$116.70
Purchase #5	$192.46	7.168%	$206.2555	$206.26	$206.25	$206.30
Purchase #6	$58.35	5.727%	$61.6917	$61.69	$61.70	$61.70
Purchase #7	$78.49	13.812%	$89.331	$89.33	$89.35	$89.30
7 purchase totals =	$900.85		$967.2711	$967.28	$967.30	$967.30