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	$39.86	13.273%	$45.1506	$45.15	$45.15	$45.20
Purchase #2	$184.69	8.536%	$200.4551	$200.46	$200.45	$200.50
Purchase #3	$29.79	9.121%	$32.5071	$32.51	$32.50	$32.50
Purchase #4	$117.49	9.343%	$128.4671	$128.47	$128.45	$128.50
Purchase #5	$74.36	13.625%	$84.4916	$84.49	$84.50	$84.50
Purchase #6	$29.41	12.584%	$33.111	$33.11	$33.10	$33.10
Purchase #7	$10.80	13.262%	$12.2323	$12.23	$12.25	$12.20
7 purchase totals =	$486.40		$536.4148	$536.42	$536.40	$536.50