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	$121.97	13.219%	$138.0932	$138.09	$138.10	$138.10
Purchase #2	$106.26	4.766%	$111.3244	$111.32	$111.30	$111.30
Purchase #3	$78.78	13.599%	$89.4933	$89.49	$89.50	$89.50
Purchase #4	$160.38	12.762%	$180.8477	$180.85	$180.85	$180.80
Purchase #5	$190.40	4.830%	$199.5963	$199.60	$199.60	$199.60
Purchase #6	$188.47	4.220%	$196.4234	$196.42	$196.40	$196.40
Purchase #7	$244.39	10.402%	$269.8114	$269.81	$269.80	$269.80
7 purchase totals =	$1,090.65		$1,185.5897	$1,185.58	$1,185.55	$1,185.50