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	$80.74	11.449%	$89.9839	$89.98	$90.00	$90.00
Purchase #2	$94.94	10.116%	$104.5441	$104.54	$104.55	$104.50
Purchase #3	$101.45	9.505%	$111.0928	$111.09	$111.10	$111.10
Purchase #4	$180.56	13.215%	$204.421	$204.42	$204.40	$204.40
Purchase #5	$223.40	12.600%	$251.5484	$251.55	$251.55	$251.50
Purchase #6	$225.75	10.402%	$249.2325	$249.23	$249.25	$249.20
Purchase #7	$173.51	5.641%	$183.2977	$183.30	$183.30	$183.30
7 purchase totals =	$1,080.35		$1,194.1204	$1,194.11	$1,194.15	$1,194.00