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	$171.40	9.637%	$187.9178	$187.92	$187.90	$187.90
Purchase #2	$222.47	5.240%	$234.1274	$234.13	$234.15	$234.10
Purchase #3	$165.66	13.305%	$187.7011	$187.70	$187.70	$187.70
Purchase #4	$41.37	3.259%	$42.7182	$42.72	$42.70	$42.70
Purchase #5	$205.69	13.613%	$233.6906	$233.69	$233.70	$233.70
Purchase #6	$213.61	4.606%	$223.4489	$223.45	$223.45	$223.40
Purchase #7	$145.92	4.338%	$152.25	$152.25	$152.25	$152.30
7 purchase totals =	$1,166.12		$1,261.8540	$1,261.86	$1,261.85	$1,261.80