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	$11.94	5.822%	$12.6351	$12.64	$12.65	$12.60
Purchase #2	$108.75	10.873%	$120.5744	$120.57	$120.55	$120.60
Purchase #3	$16.52	3.816%	$17.1504	$17.15	$17.15	$17.20
Purchase #4	$93.54	10.810%	$103.6517	$103.65	$103.65	$103.70
Purchase #5	$80.42	11.696%	$89.8259	$89.83	$89.85	$89.80
Purchase #6	$96.69	7.236%	$103.6865	$103.69	$103.70	$103.70
Purchase #7	$206.47	6.399%	$219.682	$219.68	$219.70	$219.70
7 purchase totals =	$614.33		$667.2060	$667.21	$667.25	$667.30