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	$68.52	13.669%	$77.886	$77.89	$77.90	$77.90
Purchase #2	$49.26	6.323%	$52.3747	$52.37	$52.35	$52.40
Purchase #3	$57.77	8.200%	$62.5071	$62.51	$62.50	$62.50
Purchase #4	$36.40	7.529%	$39.1406	$39.14	$39.15	$39.10
Purchase #5	$111.97	13.697%	$127.3065	$127.31	$127.30	$127.30
Purchase #6	$30.50	3.774%	$31.6511	$31.65	$31.65	$31.70
Purchase #7	$250.83	5.474%	$264.5604	$264.56	$264.55	$264.60
7 purchase totals =	$605.25		$655.4264	$655.43	$655.40	$655.50