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	$67.59	3.797%	$70.1564	$70.16	$70.15	$70.20
Purchase #2	$132.26	12.258%	$148.4724	$148.47	$148.45	$148.50
Purchase #3	$216.85	10.352%	$239.2983	$239.30	$239.30	$239.30
Purchase #4	$198.56	3.445%	$205.4004	$205.40	$205.40	$205.40
Purchase #5	$37.82	11.779%	$42.2748	$42.27	$42.25	$42.30
Purchase #6	$35.88	7.765%	$38.6661	$38.67	$38.65	$38.70
Purchase #7	$43.60	12.641%	$49.1115	$49.11	$49.10	$49.10
7 purchase totals =	$732.56		$793.3799	$793.38	$793.30	$793.50