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	$140.59	6.278%	$149.4162	$149.42	$149.40	$149.40
Purchase #2	$131.74	11.274%	$146.5924	$146.59	$146.60	$146.60
Purchase #3	$152.56	10.628%	$168.7741	$168.77	$168.75	$168.80
Purchase #4	$180.93	3.325%	$186.9459	$186.95	$186.95	$186.90
Purchase #5	$11.42	7.531%	$12.28	$12.28	$12.30	$12.30
Purchase #6	$99.48	11.664%	$111.0833	$111.08	$111.10	$111.10
Purchase #7	$202.55	13.291%	$229.4709	$229.47	$229.45	$229.50
7 purchase totals =	$919.27		$1,004.5628	$1,004.56	$1,004.55	$1,004.60