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	$19.40	6.272%	$20.6168	$20.62	$20.60	$20.60
Purchase #2	$54.76	13.413%	$62.105	$62.11	$62.10	$62.10
Purchase #3	$47.87	11.421%	$53.3372	$53.34	$53.35	$53.30
Purchase #4	$99.84	9.469%	$109.2938	$109.29	$109.30	$109.30
Purchase #5	$158.44	13.217%	$179.381	$179.38	$179.40	$179.40
Purchase #6	$69.40	11.794%	$77.585	$77.59	$77.60	$77.60
Purchase #7	$139.64	10.842%	$154.7798	$154.78	$154.80	$154.80
7 purchase totals =	$589.35		$657.0986	$657.11	$657.15	$657.10