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	$76.56	4.597%	$80.0795	$80.08	$80.10	$80.10
Purchase #2	$154.46	7.578%	$166.165	$166.17	$166.15	$166.20
Purchase #3	$58.33	11.443%	$65.0047	$65.00	$65.00	$65.00
Purchase #4	$144.49	4.389%	$150.8317	$150.83	$150.85	$150.80
Purchase #5	$74.71	8.508%	$81.0663	$81.07	$81.05	$81.10
Purchase #6	$31.40	13.319%	$35.5822	$35.58	$35.60	$35.60
Purchase #7	$204.47	12.336%	$229.6934	$229.69	$229.70	$229.70
7 purchase totals =	$744.42		$808.4228	$808.42	$808.45	$808.50