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	$235.84	7.488%	$253.4997	$253.50	$253.50	$253.50
Purchase #2	$156.63	6.408%	$166.6669	$166.67	$166.65	$166.70
Purchase #3	$111.44	12.699%	$125.5918	$125.59	$125.60	$125.60
Purchase #4	$228.46	12.281%	$256.5172	$256.52	$256.50	$256.50
Purchase #5	$19.54	7.149%	$20.9369	$20.94	$20.95	$20.90
Purchase #6	$216.76	7.635%	$233.3096	$233.31	$233.30	$233.30
Purchase #7	$73.86	13.624%	$83.9227	$83.92	$83.90	$83.90
7 purchase totals =	$1,042.53		$1,140.4448	$1,140.45	$1,140.40	$1,140.40