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	$73.28	6.605%	$78.1201	$78.12	$78.10	$78.10
Purchase #2	$132.71	13.724%	$150.9231	$150.92	$150.90	$150.90
Purchase #3	$12.90	3.600%	$13.3644	$13.36	$13.35	$13.40
Purchase #4	$126.50	4.285%	$131.9205	$131.92	$131.90	$131.90
Purchase #5	$154.99	8.205%	$167.7069	$167.71	$167.70	$167.70
Purchase #6	$33.47	11.222%	$37.226	$37.23	$37.25	$37.20
Purchase #7	$209.71	3.102%	$216.2152	$216.22	$216.20	$216.20
7 purchase totals =	$743.56		$795.4762	$795.48	$795.40	$795.40