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	$246.90	3.784%	$256.2427	$256.24	$256.25	$256.20
Purchase #2	$55.67	13.430%	$63.1465	$63.15	$63.15	$63.10
Purchase #3	$209.54	6.781%	$223.7489	$223.75	$223.75	$223.70
Purchase #4	$175.77	7.644%	$189.2059	$189.21	$189.20	$189.20
Purchase #5	$211.56	8.177%	$228.8593	$228.86	$228.85	$228.90
Purchase #6	$6.58	10.631%	$7.2795	$7.28	$7.30	$7.30
Purchase #7	$34.80	11.765%	$38.8942	$38.89	$38.90	$38.90
7 purchase totals =	$940.82		$1,007.3770	$1,007.38	$1,007.40	$1,007.30