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	$20.78	6.310%	$22.0912	$22.09	$22.10	$22.10
Purchase #2	$78.54	5.554%	$82.9021	$82.90	$82.90	$82.90
Purchase #3	$143.72	6.774%	$153.4556	$153.46	$153.45	$153.50
Purchase #4	$168.63	12.846%	$190.2922	$190.29	$190.30	$190.30
Purchase #5	$146.71	12.798%	$165.4859	$165.49	$165.50	$165.50
Purchase #6	$98.82	12.351%	$111.0253	$111.03	$111.05	$111.00
Purchase #7	$223.35	12.212%	$250.6255	$250.63	$250.65	$250.60
7 purchase totals =	$880.55		$975.8778	$975.89	$975.95	$975.90