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	$48.96	6.403%	$52.0949	$52.09	$52.10	$52.10
Purchase #2	$42.33	6.369%	$45.026	$45.03	$45.05	$45.00
Purchase #3	$239.50	5.748%	$253.2665	$253.27	$253.25	$253.30
Purchase #4	$105.81	13.376%	$119.9631	$119.96	$119.95	$120.00
Purchase #5	$55.55	10.308%	$61.2761	$61.28	$61.30	$61.30
Purchase #6	$59.86	10.486%	$66.1369	$66.14	$66.15	$66.10
Purchase #7	$6.39	7.335%	$6.8587	$6.86	$6.85	$6.90
7 purchase totals =	$558.40		$604.6222	$604.63	$604.65	$604.70