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	$10.37	3.416%	$10.7242	$10.72	$10.70	$10.70
Purchase #2	$182.59	5.365%	$192.386	$192.39	$192.40	$192.40
Purchase #3	$132.86	7.214%	$142.4445	$142.44	$142.45	$142.40
Purchase #4	$40.42	12.662%	$45.538	$45.54	$45.55	$45.50
Purchase #5	$17.49	11.703%	$19.5369	$19.54	$19.55	$19.50
Purchase #6	$233.25	13.501%	$264.7411	$264.74	$264.75	$264.70
Purchase #7	$105.58	8.822%	$114.8943	$114.89	$114.90	$114.90
7 purchase totals =	$722.56		$790.2650	$790.26	$790.30	$790.10