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	$160.92	10.760%	$178.235	$178.24	$178.25	$178.20
Purchase #2	$103.85	7.708%	$111.8548	$111.85	$111.85	$111.90
Purchase #3	$9.92	6.456%	$10.5604	$10.56	$10.55	$10.60
Purchase #4	$215.53	11.449%	$240.206	$240.21	$240.20	$240.20
Purchase #5	$80.29	5.275%	$84.5253	$84.53	$84.55	$84.50
Purchase #6	$59.42	11.760%	$66.4078	$66.41	$66.40	$66.40
Purchase #7	$198.50	12.428%	$223.1696	$223.17	$223.15	$223.20
7 purchase totals =	$828.43		$914.9589	$914.97	$914.95	$915.00