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	$159.86	4.205%	$166.5821	$166.58	$166.60	$166.60
Purchase #2	$16.52	12.708%	$18.6194	$18.62	$18.60	$18.60
Purchase #3	$154.92	3.215%	$159.9007	$159.90	$159.90	$159.90
Purchase #4	$225.40	7.476%	$242.2509	$242.25	$242.25	$242.30
Purchase #5	$215.95	12.152%	$242.1922	$242.19	$242.20	$242.20
Purchase #6	$130.96	10.512%	$144.7265	$144.73	$144.75	$144.70
Purchase #7	$36.89	3.642%	$38.2335	$38.23	$38.25	$38.20
7 purchase totals =	$940.50		$1,012.5053	$1,012.50	$1,012.55	$1,012.50