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	$73.68	8.502%	$79.9443	$79.94	$79.95	$79.90
Purchase #2	$225.76	13.274%	$255.7274	$255.73	$255.75	$255.70
Purchase #3	$109.72	13.726%	$124.7802	$124.78	$124.80	$124.80
Purchase #4	$172.62	7.384%	$185.3663	$185.37	$185.35	$185.40
Purchase #5	$21.50	13.397%	$24.3804	$24.38	$24.40	$24.40
Purchase #6	$72.26	11.293%	$80.4203	$80.42	$80.40	$80.40
Purchase #7	$234.87	13.548%	$266.6902	$266.69	$266.70	$266.70
7 purchase totals =	$910.41		$1,017.3091	$1,017.31	$1,017.35	$1,017.30