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	$144.93	9.522%	$158.7302	$158.73	$158.75	$158.70
Purchase #2	$118.30	11.140%	$131.4786	$131.48	$131.50	$131.50
Purchase #3	$141.82	4.817%	$148.6515	$148.65	$148.65	$148.70
Purchase #4	$129.32	3.803%	$134.238	$134.24	$134.25	$134.20
Purchase #5	$61.73	5.147%	$64.9072	$64.91	$64.90	$64.90
Purchase #6	$17.69	6.835%	$18.8991	$18.90	$18.90	$18.90
Purchase #7	$204.43	11.683%	$228.3136	$228.31	$228.30	$228.30
7 purchase totals =	$818.22		$885.2182	$885.22	$885.25	$885.20