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	$86.58	4.390%	$90.3809	$90.38	$90.40	$90.40
Purchase #2	$139.80	13.332%	$158.4381	$158.44	$158.45	$158.40
Purchase #3	$48.68	9.826%	$53.4633	$53.46	$53.45	$53.50
Purchase #4	$239.80	4.722%	$251.1234	$251.12	$251.10	$251.10
Purchase #5	$77.30	3.458%	$79.973	$79.97	$79.95	$80.00
Purchase #6	$165.42	5.441%	$174.4205	$174.42	$174.40	$174.40
Purchase #7	$160.66	7.517%	$172.7368	$172.74	$172.75	$172.70
7 purchase totals =	$918.24		$980.5360	$980.53	$980.50	$980.50