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	$95.51	5.198%	$100.4746	$100.47	$100.45	$100.50
Purchase #2	$163.99	9.456%	$179.4969	$179.50	$179.50	$179.50
Purchase #3	$127.56	10.843%	$141.3913	$141.39	$141.40	$141.40
Purchase #4	$45.66	11.419%	$50.8739	$50.87	$50.85	$50.90
Purchase #5	$131.58	6.636%	$140.3116	$140.31	$140.30	$140.30
Purchase #6	$19.75	9.653%	$21.6565	$21.66	$21.65	$21.70
Purchase #7	$6.86	13.458%	$7.7832	$7.78	$7.80	$7.80
7 purchase totals =	$590.91		$641.9880	$641.98	$641.95	$642.10