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	$47.92	11.872%	$53.6091	$53.61	$53.60	$53.60
Purchase #2	$150.46	11.470%	$167.7178	$167.72	$167.70	$167.70
Purchase #3	$233.49	6.834%	$249.4467	$249.45	$249.45	$249.40
Purchase #4	$172.26	5.830%	$182.3028	$182.30	$182.30	$182.30
Purchase #5	$54.57	5.294%	$57.4589	$57.46	$57.45	$57.50
Purchase #6	$90.87	10.604%	$100.5059	$100.51	$100.50	$100.50
Purchase #7	$127.37	5.828%	$134.7931	$134.79	$134.80	$134.80
7 purchase totals =	$876.94		$945.8343	$945.84	$945.80	$945.80