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	$25.25	12.207%	$28.3323	$28.33	$28.35	$28.30
Purchase #2	$148.59	13.481%	$168.6214	$168.62	$168.60	$168.60
Purchase #3	$59.61	13.763%	$67.8141	$67.81	$67.80	$67.80
Purchase #4	$16.55	13.120%	$18.7214	$18.72	$18.70	$18.70
Purchase #5	$249.72	10.388%	$275.6609	$275.66	$275.65	$275.70
Purchase #6	$82.93	4.602%	$86.7464	$86.75	$86.75	$86.70
Purchase #7	$53.77	7.710%	$57.9157	$57.92	$57.90	$57.90
7 purchase totals =	$636.42		$703.8122	$703.81	$703.75	$703.70