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	$20.51	6.600%	$21.8637	$21.86	$21.85	$21.90
Purchase #2	$45.53	11.251%	$50.6526	$50.65	$50.65	$50.70
Purchase #3	$160.57	3.317%	$165.8961	$165.90	$165.90	$165.90
Purchase #4	$138.94	12.742%	$156.6437	$156.64	$156.65	$156.60
Purchase #5	$127.97	10.807%	$141.7997	$141.80	$141.80	$141.80
Purchase #6	$76.74	4.298%	$80.0383	$80.04	$80.05	$80.00
Purchase #7	$196.68	13.196%	$222.6339	$222.63	$222.65	$222.60
7 purchase totals =	$766.94		$839.5280	$839.52	$839.55	$839.50