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	$18.73	11.384%	$20.8622	$20.86	$20.85	$20.90
Purchase #2	$88.63	8.144%	$95.848	$95.85	$95.85	$95.80
Purchase #3	$22.53	4.717%	$23.5927	$23.59	$23.60	$23.60
Purchase #4	$68.66	5.459%	$72.4081	$72.41	$72.40	$72.40
Purchase #5	$121.76	9.643%	$133.5013	$133.50	$133.50	$133.50
Purchase #6	$134.44	3.584%	$139.2583	$139.26	$139.25	$139.30
Purchase #7	$72.53	13.429%	$82.2701	$82.27	$82.25	$82.30
7 purchase totals =	$527.28		$567.7407	$567.74	$567.70	$567.80