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	$6.84	9.481%	$7.4885	$7.49	$7.50	$7.50
Purchase #2	$118.35	13.355%	$134.1556	$134.16	$134.15	$134.20
Purchase #3	$199.41	4.543%	$208.4692	$208.47	$208.45	$208.50
Purchase #4	$100.60	13.580%	$114.2615	$114.26	$114.25	$114.30
Purchase #5	$199.68	4.644%	$208.9531	$208.95	$208.95	$209.00
Purchase #6	$57.50	10.598%	$63.5939	$63.59	$63.60	$63.60
Purchase #7	$80.43	10.807%	$89.1221	$89.12	$89.10	$89.10
7 purchase totals =	$762.81		$826.0439	$826.04	$826.00	$826.20