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	$6.36	13.680%	$7.23	$7.23	$7.25	$7.20
Purchase #2	$118.77	7.728%	$127.9485	$127.95	$127.95	$127.90
Purchase #3	$96.79	9.717%	$106.1951	$106.20	$106.20	$106.20
Purchase #4	$138.99	8.648%	$151.0099	$151.01	$151.00	$151.00
Purchase #5	$149.61	4.563%	$156.4367	$156.44	$156.45	$156.40
Purchase #6	$97.77	11.282%	$108.8004	$108.80	$108.80	$108.80
Purchase #7	$116.36	13.335%	$131.8766	$131.88	$131.90	$131.90
7 purchase totals =	$724.65		$789.4972	$789.51	$789.55	$789.40