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	$40.65	7.775%	$43.8105	$43.81	$43.80	$43.80
Purchase #2	$53.32	12.197%	$59.8234	$59.82	$59.80	$59.80
Purchase #3	$230.84	12.529%	$259.7619	$259.76	$259.75	$259.80
Purchase #4	$13.53	4.166%	$14.0937	$14.09	$14.10	$14.10
Purchase #5	$12.93	5.373%	$13.6247	$13.62	$13.60	$13.60
Purchase #6	$89.76	12.346%	$100.8418	$100.84	$100.85	$100.80
Purchase #7	$113.98	13.512%	$129.381	$129.38	$129.40	$129.40
7 purchase totals =	$555.01		$621.3370	$621.32	$621.30	$621.30