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	$172.35	6.705%	$183.9061	$183.91	$183.90	$183.90
Purchase #2	$55.60	9.822%	$61.061	$61.06	$61.05	$61.10
Purchase #3	$10.87	6.309%	$11.5558	$11.56	$11.55	$11.60
Purchase #4	$212.87	3.277%	$219.8457	$219.85	$219.85	$219.80
Purchase #5	$62.72	9.113%	$68.4357	$68.44	$68.45	$68.40
Purchase #6	$40.98	10.560%	$45.3075	$45.31	$45.30	$45.30
Purchase #7	$12.78	5.756%	$13.5156	$13.52	$13.50	$13.50
7 purchase totals =	$568.17		$603.6274	$603.65	$603.60	$603.60