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	$156.50	13.650%	$177.8623	$177.86	$177.85	$177.90
Purchase #2	$248.30	6.640%	$264.7871	$264.79	$264.80	$264.80
Purchase #3	$39.86	8.265%	$43.1544	$43.15	$43.15	$43.20
Purchase #4	$16.27	9.379%	$17.796	$17.80	$17.80	$17.80
Purchase #5	$52.81	13.244%	$59.8042	$59.80	$59.80	$59.80
Purchase #6	$242.89	12.635%	$273.5792	$273.58	$273.60	$273.60
Purchase #7	$55.44	3.385%	$57.3166	$57.32	$57.30	$57.30
7 purchase totals =	$812.07		$894.2998	$894.30	$894.30	$894.40