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	$127.69	9.479%	$139.7937	$139.79	$139.80	$139.80
Purchase #2	$123.36	13.818%	$140.4059	$140.41	$140.40	$140.40
Purchase #3	$108.83	13.128%	$123.1172	$123.12	$123.10	$123.10
Purchase #4	$116.34	9.304%	$127.1643	$127.16	$127.15	$127.20
Purchase #5	$161.97	11.575%	$180.718	$180.72	$180.70	$180.70
Purchase #6	$27.87	5.743%	$29.4706	$29.47	$29.45	$29.50
Purchase #7	$111.97	7.642%	$120.5267	$120.53	$120.55	$120.50
7 purchase totals =	$778.03		$861.1964	$861.20	$861.15	$861.20