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	$11.85	10.133%	$13.0508	$13.05	$13.05	$13.10
Purchase #2	$242.91	6.839%	$259.5226	$259.52	$259.50	$259.50
Purchase #3	$50.69	10.602%	$56.0642	$56.06	$56.05	$56.10
Purchase #4	$237.33	13.391%	$269.1109	$269.11	$269.10	$269.10
Purchase #5	$23.96	9.766%	$26.2999	$26.30	$26.30	$26.30
Purchase #6	$83.68	6.738%	$89.3184	$89.32	$89.30	$89.30
Purchase #7	$65.46	10.351%	$72.2358	$72.24	$72.25	$72.20
7 purchase totals =	$715.88		$785.6026	$785.60	$785.55	$785.60