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	$10.47	11.811%	$11.7066	$11.71	$11.70	$11.70
Purchase #2	$195.68	13.544%	$222.1829	$222.18	$222.20	$222.20
Purchase #3	$168.45	10.205%	$185.6403	$185.64	$185.65	$185.60
Purchase #4	$149.29	7.441%	$160.3987	$160.40	$160.40	$160.40
Purchase #5	$233.43	13.296%	$264.4669	$264.47	$264.45	$264.50
Purchase #6	$42.75	13.618%	$48.5717	$48.57	$48.55	$48.60
Purchase #7	$6.93	5.110%	$7.2841	$7.28	$7.30	$7.30
7 purchase totals =	$807.00		$900.2512	$900.25	$900.25	$900.30