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	$150.87	13.306%	$170.9448	$170.94	$170.95	$170.90
Purchase #2	$153.52	11.361%	$170.9614	$170.96	$170.95	$171.00
Purchase #3	$69.83	13.660%	$79.3688	$79.37	$79.35	$79.40
Purchase #4	$247.74	4.781%	$259.5844	$259.58	$259.60	$259.60
Purchase #5	$225.82	5.675%	$238.6353	$238.64	$238.65	$238.60
Purchase #6	$39.83	6.764%	$42.5241	$42.52	$42.50	$42.50
Purchase #7	$51.63	11.340%	$57.4848	$57.48	$57.50	$57.50
7 purchase totals =	$939.24		$1,019.5036	$1,019.49	$1,019.50	$1,019.50