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	$212.39	6.557%	$226.3164	$226.32	$226.30	$226.30
Purchase #2	$137.70	6.323%	$146.4068	$146.41	$146.40	$146.40
Purchase #3	$168.77	12.447%	$189.7768	$189.78	$189.80	$189.80
Purchase #4	$9.91	8.762%	$10.7783	$10.78	$10.80	$10.80
Purchase #5	$193.58	10.747%	$214.384	$214.38	$214.40	$214.40
Purchase #6	$201.80	13.809%	$229.6666	$229.67	$229.65	$229.70
Purchase #7	$78.68	4.384%	$82.1293	$82.13	$82.15	$82.10
7 purchase totals =	$1,002.83		$1,099.4582	$1,099.47	$1,099.50	$1,099.50