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	$89.80	11.637%	$100.25	$100.25	$100.25	$100.30
Purchase #2	$58.52	6.686%	$62.4326	$62.43	$62.45	$62.40
Purchase #3	$28.96	4.382%	$30.229	$30.23	$30.25	$30.20
Purchase #4	$216.54	5.648%	$228.7702	$228.77	$228.75	$228.80
Purchase #5	$233.65	4.608%	$244.4166	$244.42	$244.40	$244.40
Purchase #6	$47.67	6.812%	$50.9173	$50.92	$50.90	$50.90
Purchase #7	$6.73	7.498%	$7.2346	$7.23	$7.25	$7.20
7 purchase totals =	$681.87		$724.2503	$724.25	$724.25	$724.20