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	$245.97	13.233%	$278.5192	$278.52	$278.50	$278.50
Purchase #2	$99.95	3.234%	$103.1824	$103.18	$103.20	$103.20
Purchase #3	$33.84	10.724%	$37.469	$37.47	$37.45	$37.50
Purchase #4	$91.37	4.855%	$95.806	$95.81	$95.80	$95.80
Purchase #5	$232.86	3.592%	$241.2243	$241.22	$241.20	$241.20
Purchase #6	$209.43	6.612%	$223.2775	$223.28	$223.30	$223.30
Purchase #7	$149.29	12.239%	$167.5616	$167.56	$167.55	$167.60
7 purchase totals =	$1,062.71		$1,147.0400	$1,147.04	$1,147.00	$1,147.10