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	$66.77	10.167%	$73.5585	$73.56	$73.55	$73.60
Purchase #2	$141.30	6.206%	$150.0691	$150.07	$150.05	$150.10
Purchase #3	$221.59	12.808%	$249.9712	$249.97	$249.95	$250.00
Purchase #4	$19.77	3.822%	$20.5256	$20.53	$20.55	$20.50
Purchase #5	$138.51	4.766%	$145.1114	$145.11	$145.10	$145.10
Purchase #6	$111.49	6.123%	$118.3165	$118.32	$118.30	$118.30
Purchase #7	$237.56	4.192%	$247.5185	$247.52	$247.50	$247.50
7 purchase totals =	$936.99		$1,005.0708	$1,005.08	$1,005.00	$1,005.10