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	$135.56	8.616%	$147.2398	$147.24	$147.25	$147.20
Purchase #2	$123.71	13.387%	$140.2711	$140.27	$140.25	$140.30
Purchase #3	$247.88	12.271%	$278.2974	$278.30	$278.30	$278.30
Purchase #4	$47.87	9.482%	$52.409	$52.41	$52.40	$52.40
Purchase #5	$105.60	4.649%	$110.5093	$110.51	$110.50	$110.50
Purchase #6	$51.29	11.707%	$57.2945	$57.29	$57.30	$57.30
Purchase #7	$96.27	7.532%	$103.5211	$103.52	$103.50	$103.50
7 purchase totals =	$808.18		$889.5422	$889.54	$889.50	$889.50