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	$85.93	6.477%	$91.4957	$91.50	$91.50	$91.50
Purchase #2	$98.61	12.713%	$111.1463	$111.15	$111.15	$111.10
Purchase #3	$32.84	11.175%	$36.5099	$36.51	$36.50	$36.50
Purchase #4	$173.44	3.849%	$180.1157	$180.12	$180.10	$180.10
Purchase #5	$170.50	9.436%	$186.5884	$186.59	$186.60	$186.60
Purchase #6	$19.84	7.396%	$21.3074	$21.31	$21.30	$21.30
Purchase #7	$53.52	13.370%	$60.6756	$60.68	$60.70	$60.70
7 purchase totals =	$634.68		$687.8390	$687.86	$687.85	$687.80