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	$78.85	13.404%	$89.4191	$89.42	$89.40	$89.40
Purchase #2	$159.77	9.232%	$174.52	$174.52	$174.50	$174.50
Purchase #3	$96.50	11.607%	$107.7008	$107.70	$107.70	$107.70
Purchase #4	$95.28	12.536%	$107.2243	$107.22	$107.20	$107.20
Purchase #5	$43.69	6.237%	$46.4149	$46.41	$46.40	$46.40
Purchase #6	$42.80	13.641%	$48.6383	$48.64	$48.65	$48.60
Purchase #7	$190.66	10.580%	$210.8318	$210.83	$210.85	$210.80
7 purchase totals =	$707.55		$784.7492	$784.74	$784.70	$784.60