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	$56.66	8.389%	$61.4132	$61.41	$61.40	$61.40
Purchase #2	$37.32	12.717%	$42.066	$42.07	$42.05	$42.10
Purchase #3	$84.26	8.323%	$91.273	$91.27	$91.25	$91.30
Purchase #4	$43.46	12.647%	$48.9564	$48.96	$48.95	$49.00
Purchase #5	$10.93	10.223%	$12.0474	$12.05	$12.05	$12.00
Purchase #6	$157.60	4.230%	$164.2665	$164.27	$164.25	$164.30
Purchase #7	$189.64	13.537%	$215.3116	$215.31	$215.30	$215.30
7 purchase totals =	$579.87		$635.3341	$635.34	$635.25	$635.40