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	$51.59	7.266%	$55.3385	$55.34	$55.35	$55.30
Purchase #2	$92.72	8.788%	$100.8682	$100.87	$100.85	$100.90
Purchase #3	$198.68	12.560%	$223.6342	$223.63	$223.65	$223.60
Purchase #4	$94.61	13.743%	$107.6123	$107.61	$107.60	$107.60
Purchase #5	$103.99	7.290%	$111.5709	$111.57	$111.55	$111.60
Purchase #6	$185.72	12.177%	$208.3351	$208.34	$208.35	$208.30
Purchase #7	$57.37	6.139%	$60.8919	$60.89	$60.90	$60.90
7 purchase totals =	$784.68		$868.2511	$868.25	$868.25	$868.20