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	$78.94	9.229%	$86.2254	$86.23	$86.25	$86.20
Purchase #2	$250.86	12.377%	$281.9089	$281.91	$281.90	$281.90
Purchase #3	$185.92	7.285%	$199.4643	$199.46	$199.45	$199.50
Purchase #4	$64.71	3.145%	$66.7451	$66.75	$66.75	$66.70
Purchase #5	$153.60	4.384%	$160.3338	$160.33	$160.35	$160.30
Purchase #6	$129.26	3.244%	$133.4532	$133.45	$133.45	$133.50
Purchase #7	$45.64	5.850%	$48.3099	$48.31	$48.30	$48.30
7 purchase totals =	$908.93		$976.4406	$976.44	$976.45	$976.40