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	$64.64	7.238%	$69.3186	$69.32	$69.30	$69.30
Purchase #2	$78.64	13.707%	$89.4192	$89.42	$89.40	$89.40
Purchase #3	$116.61	10.538%	$128.8984	$128.90	$128.90	$128.90
Purchase #4	$81.27	6.770%	$86.772	$86.77	$86.75	$86.80
Purchase #5	$30.91	12.627%	$34.813	$34.81	$34.80	$34.80
Purchase #6	$60.32	12.225%	$67.6941	$67.69	$67.70	$67.70
Purchase #7	$111.50	4.752%	$116.7985	$116.80	$116.80	$116.80
7 purchase totals =	$543.89		$593.7138	$593.71	$593.65	$593.70