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	$39.98	13.158%	$45.2406	$45.24	$45.25	$45.20
Purchase #2	$224.83	13.500%	$255.1821	$255.18	$255.20	$255.20
Purchase #3	$204.59	8.208%	$221.3827	$221.38	$221.40	$221.40
Purchase #4	$130.33	9.420%	$142.6071	$142.61	$142.60	$142.60
Purchase #5	$128.79	8.223%	$139.3804	$139.38	$139.40	$139.40
Purchase #6	$39.96	12.423%	$44.9242	$44.92	$44.90	$44.90
Purchase #7	$33.44	7.361%	$35.9015	$35.90	$35.90	$35.90
7 purchase totals =	$801.92		$884.6186	$884.61	$884.65	$884.60