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	$57.89	3.595%	$59.9711	$59.97	$59.95	$60.00
Purchase #2	$79.45	5.473%	$83.7983	$83.80	$83.80	$83.80
Purchase #3	$42.27	5.193%	$44.4651	$44.47	$44.45	$44.50
Purchase #4	$97.47	11.410%	$108.5913	$108.59	$108.60	$108.60
Purchase #5	$134.30	7.350%	$144.1711	$144.17	$144.15	$144.20
Purchase #6	$87.25	6.161%	$92.6255	$92.63	$92.65	$92.60
Purchase #7	$101.71	10.588%	$112.4791	$112.48	$112.50	$112.50
7 purchase totals =	$600.34		$646.1015	$646.11	$646.10	$646.20