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	$74.90	8.321%	$81.1324	$81.13	$81.15	$81.10
Purchase #2	$86.87	3.746%	$90.1242	$90.12	$90.10	$90.10
Purchase #3	$47.66	10.596%	$52.7101	$52.71	$52.70	$52.70
Purchase #4	$113.42	12.376%	$127.4569	$127.46	$127.45	$127.50
Purchase #5	$25.96	11.814%	$29.0269	$29.03	$29.05	$29.00
Purchase #6	$189.96	11.216%	$211.2659	$211.27	$211.25	$211.30
Purchase #7	$35.49	7.471%	$38.1415	$38.14	$38.15	$38.10
7 purchase totals =	$574.26		$629.8579	$629.86	$629.85	$629.80