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	$84.92	7.777%	$91.5242	$91.52	$91.50	$91.50
Purchase #2	$40.89	13.108%	$46.2499	$46.25	$46.25	$46.20
Purchase #3	$150.29	9.311%	$164.2835	$164.28	$164.30	$164.30
Purchase #4	$105.84	7.516%	$113.7949	$113.79	$113.80	$113.80
Purchase #5	$148.98	5.192%	$156.715	$156.72	$156.70	$156.70
Purchase #6	$127.27	12.230%	$142.8351	$142.84	$142.85	$142.80
Purchase #7	$83.64	10.348%	$92.2951	$92.30	$92.30	$92.30
7 purchase totals =	$741.83		$807.6977	$807.70	$807.70	$807.60