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	$233.79	8.820%	$254.4103	$254.41	$254.40	$254.40
Purchase #2	$18.54	5.197%	$19.5035	$19.50	$19.50	$19.50
Purchase #3	$225.59	8.394%	$244.526	$244.53	$244.55	$244.50
Purchase #4	$28.97	3.326%	$29.9335	$29.93	$29.95	$29.90
Purchase #5	$223.61	10.134%	$246.2706	$246.27	$246.25	$246.30
Purchase #6	$107.54	3.807%	$111.634	$111.63	$111.65	$111.60
Purchase #7	$71.84	9.400%	$78.593	$78.59	$78.60	$78.60
7 purchase totals =	$909.88		$984.8709	$984.86	$984.90	$984.80