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	$214.95	12.183%	$241.1374	$241.14	$241.15	$241.10
Purchase #2	$84.71	8.175%	$91.635	$91.64	$91.65	$91.60
Purchase #3	$37.69	12.696%	$42.4751	$42.48	$42.50	$42.50
Purchase #4	$119.80	11.192%	$133.208	$133.21	$133.20	$133.20
Purchase #5	$45.38	13.103%	$51.3261	$51.33	$51.35	$51.30
Purchase #6	$156.44	11.745%	$174.8139	$174.81	$174.80	$174.80
Purchase #7	$133.56	6.708%	$142.5192	$142.52	$142.50	$142.50
7 purchase totals =	$792.53		$877.1147	$877.13	$877.15	$877.00