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	$166.88	13.152%	$188.8281	$188.83	$188.85	$188.80
Purchase #2	$173.73	12.764%	$195.9049	$195.90	$195.90	$195.90
Purchase #3	$97.96	13.539%	$111.2228	$111.22	$111.20	$111.20
Purchase #4	$67.92	3.812%	$70.5091	$70.51	$70.50	$70.50
Purchase #5	$91.51	11.298%	$101.8488	$101.85	$101.85	$101.80
Purchase #6	$224.86	12.336%	$252.5987	$252.60	$252.60	$252.60
Purchase #7	$20.70	5.538%	$21.8464	$21.85	$21.85	$21.80
7 purchase totals =	$843.56		$942.7588	$942.76	$942.75	$942.60