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	$100.98	10.516%	$111.5991	$111.60	$111.60	$111.60
Purchase #2	$222.26	5.128%	$233.6575	$233.66	$233.65	$233.70
Purchase #3	$242.69	8.499%	$263.3162	$263.32	$263.30	$263.30
Purchase #4	$98.79	3.161%	$101.9128	$101.91	$101.90	$101.90
Purchase #5	$221.50	9.190%	$241.8559	$241.86	$241.85	$241.90
Purchase #6	$35.84	10.415%	$39.5727	$39.57	$39.55	$39.60
Purchase #7	$52.70	8.315%	$57.082	$57.08	$57.10	$57.10
7 purchase totals =	$974.76		$1,048.9962	$1,049.00	$1,048.95	$1,049.10