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	$80.36	10.851%	$89.0799	$89.08	$89.10	$89.10
Purchase #2	$129.61	13.795%	$147.4897	$147.49	$147.50	$147.50
Purchase #3	$71.92	10.141%	$79.2134	$79.21	$79.20	$79.20
Purchase #4	$71.57	12.661%	$80.6315	$80.63	$80.65	$80.60
Purchase #5	$107.36	6.540%	$114.3813	$114.38	$114.40	$114.40
Purchase #6	$99.30	6.528%	$105.7823	$105.78	$105.80	$105.80
Purchase #7	$78.52	10.589%	$86.8345	$86.83	$86.85	$86.80
7 purchase totals =	$638.64		$703.4126	$703.40	$703.50	$703.40