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	$62.90	13.198%	$71.2015	$71.20	$71.20	$71.20
Purchase #2	$143.87	8.312%	$155.8285	$155.83	$155.85	$155.80
Purchase #3	$85.28	4.640%	$89.237	$89.24	$89.25	$89.20
Purchase #4	$154.62	8.623%	$167.9529	$167.95	$167.95	$168.00
Purchase #5	$138.83	3.390%	$143.5363	$143.54	$143.55	$143.50
Purchase #6	$158.99	4.749%	$166.5404	$166.54	$166.55	$166.50
Purchase #7	$51.93	3.616%	$53.8078	$53.81	$53.80	$53.80
7 purchase totals =	$796.42		$848.1044	$848.11	$848.15	$848.00