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	$10.74	6.346%	$11.4216	$11.42	$11.40	$11.40
Purchase #2	$187.75	9.685%	$205.9336	$205.93	$205.95	$205.90
Purchase #3	$104.51	12.216%	$117.2769	$117.28	$117.30	$117.30
Purchase #4	$174.65	12.234%	$196.0167	$196.02	$196.00	$196.00
Purchase #5	$54.49	10.706%	$60.3237	$60.32	$60.30	$60.30
Purchase #6	$94.95	9.261%	$103.7433	$103.74	$103.75	$103.70
Purchase #7	$52.73	3.289%	$54.4643	$54.46	$54.45	$54.50
7 purchase totals =	$679.82		$749.1801	$749.17	$749.15	$749.10