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	$51.71	12.350%	$58.0962	$58.10	$58.10	$58.10
Purchase #2	$162.60	4.628%	$170.1251	$170.13	$170.15	$170.10
Purchase #3	$26.25	7.522%	$28.2245	$28.22	$28.20	$28.20
Purchase #4	$105.38	12.113%	$118.1447	$118.14	$118.15	$118.10
Purchase #5	$78.94	8.685%	$85.7959	$85.80	$85.80	$85.80
Purchase #6	$128.27	9.721%	$140.7391	$140.74	$140.75	$140.70
Purchase #7	$113.83	11.633%	$127.0718	$127.07	$127.05	$127.10
7 purchase totals =	$666.98		$728.1973	$728.20	$728.20	$728.10