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	$25.82	7.649%	$27.795	$27.80	$27.80	$27.80
Purchase #2	$67.89	3.575%	$70.3171	$70.32	$70.30	$70.30
Purchase #3	$237.25	5.487%	$250.2679	$250.27	$250.25	$250.30
Purchase #4	$17.81	4.873%	$18.6779	$18.68	$18.70	$18.70
Purchase #5	$95.27	5.729%	$100.728	$100.73	$100.75	$100.70
Purchase #6	$59.55	13.154%	$67.3832	$67.38	$67.40	$67.40
Purchase #7	$58.44	5.388%	$61.5887	$61.59	$61.60	$61.60
7 purchase totals =	$562.03		$596.7578	$596.77	$596.80	$596.80