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	$90.38	13.809%	$102.8606	$102.86	$102.85	$102.90
Purchase #2	$178.27	7.289%	$191.2641	$191.26	$191.25	$191.30
Purchase #3	$91.80	13.858%	$104.5216	$104.52	$104.50	$104.50
Purchase #4	$70.65	12.678%	$79.607	$79.61	$79.60	$79.60
Purchase #5	$118.41	5.408%	$124.8136	$124.81	$124.80	$124.80
Purchase #6	$158.33	11.144%	$175.9743	$175.97	$175.95	$176.00
Purchase #7	$36.33	4.245%	$37.8722	$37.87	$37.85	$37.90
7 purchase totals =	$744.17		$816.9134	$816.90	$816.80	$817.00