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	$122.35	13.541%	$138.9174	$138.92	$138.90	$138.90
Purchase #2	$70.82	9.272%	$77.3864	$77.39	$77.40	$77.40
Purchase #3	$43.83	4.813%	$45.9395	$45.94	$45.95	$45.90
Purchase #4	$142.75	4.310%	$148.9025	$148.90	$148.90	$148.90
Purchase #5	$101.32	3.711%	$105.08	$105.08	$105.10	$105.10
Purchase #6	$134.95	4.731%	$141.3345	$141.33	$141.35	$141.30
Purchase #7	$38.25	12.303%	$42.9559	$42.96	$42.95	$43.00
7 purchase totals =	$654.27		$700.5162	$700.52	$700.55	$700.50