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	$24.28	11.747%	$27.1322	$27.13	$27.15	$27.10
Purchase #2	$141.40	10.199%	$155.8214	$155.82	$155.80	$155.80
Purchase #3	$43.81	6.374%	$46.6024	$46.60	$46.60	$46.60
Purchase #4	$54.90	8.527%	$59.5813	$59.58	$59.60	$59.60
Purchase #5	$127.49	9.614%	$139.7469	$139.75	$139.75	$139.70
Purchase #6	$182.52	3.353%	$188.6399	$188.64	$188.65	$188.60
Purchase #7	$11.71	6.817%	$12.5083	$12.51	$12.50	$12.50
7 purchase totals =	$586.11		$630.0324	$630.03	$630.05	$629.90