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	$6.62	4.314%	$6.9056	$6.91	$6.90	$6.90
Purchase #2	$119.91	6.510%	$127.7161	$127.72	$127.70	$127.70
Purchase #3	$179.59	4.792%	$188.196	$188.20	$188.20	$188.20
Purchase #4	$176.35	5.231%	$185.5749	$185.57	$185.55	$185.60
Purchase #5	$75.74	10.152%	$83.4291	$83.43	$83.45	$83.40
Purchase #6	$230.25	4.531%	$240.6826	$240.68	$240.70	$240.70
Purchase #7	$142.98	13.723%	$162.6011	$162.60	$162.60	$162.60
7 purchase totals =	$931.44		$995.1054	$995.11	$995.10	$995.10