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	$144.49	7.775%	$155.7241	$155.72	$155.70	$155.70
Purchase #2	$213.35	5.420%	$224.9136	$224.91	$224.90	$224.90
Purchase #3	$48.58	12.250%	$54.5311	$54.53	$54.55	$54.50
Purchase #4	$115.40	10.393%	$127.3935	$127.39	$127.40	$127.40
Purchase #5	$85.95	7.613%	$92.4934	$92.49	$92.50	$92.50
Purchase #6	$97.93	13.786%	$111.4306	$111.43	$111.45	$111.40
Purchase #7	$117.79	13.742%	$133.9767	$133.98	$134.00	$134.00
7 purchase totals =	$823.49		$900.4630	$900.45	$900.50	$900.40