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	$117.55	13.109%	$132.9596	$132.96	$132.95	$133.00
Purchase #2	$58.76	5.711%	$62.1158	$62.12	$62.10	$62.10
Purchase #3	$223.57	4.593%	$233.8386	$233.84	$233.85	$233.80
Purchase #4	$95.70	8.585%	$103.9158	$103.92	$103.90	$103.90
Purchase #5	$191.42	5.592%	$202.1242	$202.12	$202.10	$202.10
Purchase #6	$41.59	9.285%	$45.4516	$45.45	$45.45	$45.50
Purchase #7	$40.93	3.779%	$42.4767	$42.48	$42.50	$42.50
7 purchase totals =	$769.52		$822.8823	$822.89	$822.85	$822.90