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	$173.73	3.327%	$179.51	$179.51	$179.50	$179.50
Purchase #2	$130.42	11.485%	$145.3987	$145.40	$145.40	$145.40
Purchase #3	$86.59	10.389%	$95.5858	$95.59	$95.60	$95.60
Purchase #4	$10.88	7.199%	$11.6633	$11.66	$11.65	$11.70
Purchase #5	$96.82	12.167%	$108.6001	$108.60	$108.60	$108.60
Purchase #6	$76.53	7.620%	$82.3616	$82.36	$82.35	$82.40
Purchase #7	$102.35	7.618%	$110.147	$110.15	$110.15	$110.10
7 purchase totals =	$677.32		$733.2665	$733.27	$733.25	$733.30