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	$95.81	8.717%	$104.1618	$104.16	$104.15	$104.20
Purchase #2	$39.65	4.394%	$41.3922	$41.39	$41.40	$41.40
Purchase #3	$98.47	12.869%	$111.1421	$111.14	$111.15	$111.10
Purchase #4	$83.95	6.212%	$89.165	$89.17	$89.15	$89.20
Purchase #5	$49.28	4.515%	$51.505	$51.51	$51.50	$51.50
Purchase #6	$129.65	12.441%	$145.7798	$145.78	$145.80	$145.80
Purchase #7	$7.88	4.787%	$8.2572	$8.26	$8.25	$8.30
7 purchase totals =	$504.69		$551.4031	$551.41	$551.40	$551.50