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	$44.87	6.594%	$47.8287	$47.83	$47.85	$47.80
Purchase #2	$219.91	10.122%	$242.1693	$242.17	$242.15	$242.20
Purchase #3	$77.79	7.356%	$83.5122	$83.51	$83.50	$83.50
Purchase #4	$210.67	6.241%	$223.8179	$223.82	$223.80	$223.80
Purchase #5	$36.56	7.433%	$39.2775	$39.28	$39.30	$39.30
Purchase #6	$16.83	8.668%	$18.2888	$18.29	$18.30	$18.30
Purchase #7	$106.77	5.296%	$112.4245	$112.42	$112.40	$112.40
7 purchase totals =	$713.40		$767.3189	$767.32	$767.30	$767.30