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	$64.54	10.700%	$71.4458	$71.45	$71.45	$71.40
Purchase #2	$56.38	13.325%	$63.8926	$63.89	$63.90	$63.90
Purchase #3	$185.98	10.678%	$205.8389	$205.84	$205.85	$205.80
Purchase #4	$98.73	9.658%	$108.2653	$108.27	$108.25	$108.30
Purchase #5	$219.27	8.400%	$237.6887	$237.69	$237.70	$237.70
Purchase #6	$74.50	10.483%	$82.3098	$82.31	$82.30	$82.30
Purchase #7	$141.67	8.608%	$153.865	$153.87	$153.85	$153.90
7 purchase totals =	$841.07		$923.3061	$923.32	$923.30	$923.30