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	$19.64	8.410%	$21.2917	$21.29	$21.30	$21.30
Purchase #2	$246.29	3.872%	$255.8263	$255.83	$255.85	$255.80
Purchase #3	$163.91	4.154%	$170.7188	$170.72	$170.70	$170.70
Purchase #4	$80.61	3.116%	$83.1218	$83.12	$83.10	$83.10
Purchase #5	$101.59	8.224%	$109.9448	$109.94	$109.95	$109.90
Purchase #6	$34.30	8.424%	$37.1894	$37.19	$37.20	$37.20
Purchase #7	$48.73	8.258%	$52.7541	$52.75	$52.75	$52.80
7 purchase totals =	$695.07		$730.8469	$730.84	$730.85	$730.80