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	$192.70	4.259%	$200.9071	$200.91	$200.90	$200.90
Purchase #2	$142.34	12.712%	$160.4343	$160.43	$160.45	$160.40
Purchase #3	$192.47	6.337%	$204.6668	$204.67	$204.65	$204.70
Purchase #4	$72.30	8.305%	$78.3045	$78.30	$78.30	$78.30
Purchase #5	$99.40	11.787%	$111.1163	$111.12	$111.10	$111.10
Purchase #6	$17.49	13.550%	$19.8599	$19.86	$19.85	$19.90
Purchase #7	$199.32	11.724%	$222.6883	$222.69	$222.70	$222.70
7 purchase totals =	$916.02		$997.9772	$997.98	$997.95	$998.00