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	$40.78	11.377%	$45.4195	$45.42	$45.40	$45.40
Purchase #2	$113.51	5.449%	$119.6952	$119.70	$119.70	$119.70
Purchase #3	$132.53	11.638%	$147.9538	$147.95	$147.95	$148.00
Purchase #4	$100.94	8.133%	$109.1495	$109.15	$109.15	$109.10
Purchase #5	$33.52	5.551%	$35.3807	$35.38	$35.40	$35.40
Purchase #6	$211.75	5.690%	$223.7986	$223.80	$223.80	$223.80
Purchase #7	$48.38	13.559%	$54.9398	$54.94	$54.95	$54.90
7 purchase totals =	$681.41		$736.3371	$736.34	$736.35	$736.30