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	$238.49	8.618%	$259.0431	$259.04	$259.05	$259.00
Purchase #2	$95.49	4.654%	$99.9341	$99.93	$99.95	$99.90
Purchase #3	$65.68	10.640%	$72.6684	$72.67	$72.65	$72.70
Purchase #4	$81.91	8.800%	$89.1181	$89.12	$89.10	$89.10
Purchase #5	$53.53	13.714%	$60.8711	$60.87	$60.85	$60.90
Purchase #6	$233.62	10.749%	$258.7318	$258.73	$258.75	$258.70
Purchase #7	$171.89	6.667%	$183.3499	$183.35	$183.35	$183.30
7 purchase totals =	$940.61		$1,023.7165	$1,023.71	$1,023.70	$1,023.60