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	$74.46	6.223%	$79.0936	$79.09	$79.10	$79.10
Purchase #2	$54.39	8.726%	$59.1361	$59.14	$59.15	$59.10
Purchase #3	$126.57	4.235%	$131.9302	$131.93	$131.95	$131.90
Purchase #4	$55.94	9.589%	$61.3041	$61.30	$61.30	$61.30
Purchase #5	$175.86	5.495%	$185.5235	$185.52	$185.50	$185.50
Purchase #6	$220.65	9.642%	$241.9251	$241.93	$241.95	$241.90
Purchase #7	$12.97	5.165%	$13.6399	$13.64	$13.65	$13.60
7 purchase totals =	$720.84		$772.5525	$772.55	$772.60	$772.40