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	$63.46	13.315%	$71.9097	$71.91	$71.90	$71.90
Purchase #2	$123.96	6.325%	$131.8005	$131.80	$131.80	$131.80
Purchase #3	$187.83	7.397%	$201.7238	$201.72	$201.70	$201.70
Purchase #4	$116.65	9.608%	$127.8577	$127.86	$127.85	$127.90
Purchase #5	$100.64	10.293%	$110.9989	$111.00	$111.00	$111.00
Purchase #6	$153.66	3.684%	$159.3208	$159.32	$159.30	$159.30
Purchase #7	$88.57	8.745%	$96.3154	$96.32	$96.30	$96.30
7 purchase totals =	$834.77		$899.9268	$899.93	$899.85	$899.90