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	$26.68	12.489%	$30.0121	$30.01	$30.00	$30.00
Purchase #2	$78.57	13.342%	$89.0528	$89.05	$89.05	$89.10
Purchase #3	$58.93	4.650%	$61.6702	$61.67	$61.65	$61.70
Purchase #4	$46.38	11.237%	$51.5917	$51.59	$51.60	$51.60
Purchase #5	$166.31	8.175%	$179.9058	$179.91	$179.90	$179.90
Purchase #6	$17.74	13.329%	$20.1046	$20.10	$20.10	$20.10
Purchase #7	$101.78	11.617%	$113.6038	$113.60	$113.60	$113.60
7 purchase totals =	$496.39		$545.9410	$545.93	$545.90	$546.00