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	$79.33	12.801%	$89.485	$89.49	$89.50	$89.50
Purchase #2	$54.96	6.694%	$58.639	$58.64	$58.65	$58.60
Purchase #3	$127.87	11.419%	$142.4715	$142.47	$142.45	$142.50
Purchase #4	$123.39	6.553%	$131.4757	$131.48	$131.50	$131.50
Purchase #5	$181.54	6.621%	$193.5598	$193.56	$193.55	$193.60
Purchase #6	$71.60	7.105%	$76.6872	$76.69	$76.70	$76.70
Purchase #7	$49.67	6.464%	$52.8807	$52.88	$52.90	$52.90
7 purchase totals =	$688.36		$745.1989	$745.21	$745.25	$745.30