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	$85.69	4.673%	$89.6943	$89.69	$89.70	$89.70
Purchase #2	$84.84	12.414%	$95.372	$95.37	$95.35	$95.40
Purchase #3	$49.76	12.601%	$56.0303	$56.03	$56.05	$56.00
Purchase #4	$48.88	11.351%	$54.4284	$54.43	$54.45	$54.40
Purchase #5	$37.40	6.450%	$39.8123	$39.81	$39.80	$39.80
Purchase #6	$73.29	13.849%	$83.4399	$83.44	$83.45	$83.40
Purchase #7	$131.95	8.503%	$143.1697	$143.17	$143.15	$143.20
7 purchase totals =	$511.81		$561.9469	$561.94	$561.95	$561.90