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	$92.61	7.753%	$99.7901	$99.79	$99.80	$99.80
Purchase #2	$232.42	13.217%	$263.139	$263.14	$263.15	$263.10
Purchase #3	$131.40	6.786%	$140.3168	$140.32	$140.30	$140.30
Purchase #4	$72.99	11.242%	$81.1955	$81.20	$81.20	$81.20
Purchase #5	$73.79	3.631%	$76.4693	$76.47	$76.45	$76.50
Purchase #6	$103.83	7.648%	$111.7709	$111.77	$111.75	$111.80
Purchase #7	$217.28	10.334%	$239.7337	$239.73	$239.75	$239.70
7 purchase totals =	$924.32		$1,012.4153	$1,012.42	$1,012.40	$1,012.40