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	$67.97	9.842%	$74.6596	$74.66	$74.65	$74.70
Purchase #2	$160.64	13.814%	$182.8308	$182.83	$182.85	$182.80
Purchase #3	$193.50	3.718%	$200.6943	$200.69	$200.70	$200.70
Purchase #4	$217.35	7.395%	$233.423	$233.42	$233.40	$233.40
Purchase #5	$109.78	7.650%	$118.1782	$118.18	$118.20	$118.20
Purchase #6	$127.83	6.770%	$136.4841	$136.48	$136.50	$136.50
Purchase #7	$38.65	4.165%	$40.2598	$40.26	$40.25	$40.30
7 purchase totals =	$915.72		$986.5298	$986.52	$986.55	$986.60