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	$160.30	12.154%	$179.7829	$179.78	$179.80	$179.80
Purchase #2	$139.48	4.286%	$145.4581	$145.46	$145.45	$145.50
Purchase #3	$107.28	7.548%	$115.3775	$115.38	$115.40	$115.40
Purchase #4	$115.77	13.199%	$131.0505	$131.05	$131.05	$131.10
Purchase #5	$62.35	13.501%	$70.7679	$70.77	$70.75	$70.80
Purchase #6	$228.47	4.570%	$238.9111	$238.91	$238.90	$238.90
Purchase #7	$234.36	9.133%	$255.7641	$255.76	$255.75	$255.80
7 purchase totals =	$1,048.01		$1,137.1121	$1,137.11	$1,137.10	$1,137.30