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	$107.27	10.541%	$118.5773	$118.58	$118.60	$118.60
Purchase #2	$122.53	6.657%	$130.6868	$130.69	$130.70	$130.70
Purchase #3	$59.84	9.397%	$65.4632	$65.46	$65.45	$65.50
Purchase #4	$77.34	6.399%	$82.289	$82.29	$82.30	$82.30
Purchase #5	$40.52	11.410%	$45.1433	$45.14	$45.15	$45.10
Purchase #6	$95.31	13.207%	$107.8976	$107.90	$107.90	$107.90
Purchase #7	$87.39	3.264%	$90.2424	$90.24	$90.25	$90.20
7 purchase totals =	$590.20		$640.2996	$640.30	$640.35	$640.30