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	$160.85	4.540%	$168.1526	$168.15	$168.15	$168.20
Purchase #2	$117.35	12.152%	$131.6104	$131.61	$131.60	$131.60
Purchase #3	$205.37	6.436%	$218.5876	$218.59	$218.60	$218.60
Purchase #4	$52.27	8.453%	$56.6884	$56.69	$56.70	$56.70
Purchase #5	$43.56	6.844%	$46.5412	$46.54	$46.55	$46.50
Purchase #6	$67.52	4.278%	$70.4085	$70.41	$70.40	$70.40
Purchase #7	$140.72	6.164%	$149.394	$149.39	$149.40	$149.40
7 purchase totals =	$787.64		$841.3827	$841.38	$841.40	$841.40