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	$24.81	9.166%	$27.0841	$27.08	$27.10	$27.10
Purchase #2	$147.60	11.668%	$164.822	$164.82	$164.80	$164.80
Purchase #3	$155.83	5.508%	$164.4131	$164.41	$164.40	$164.40
Purchase #4	$152.40	8.418%	$165.229	$165.23	$165.25	$165.20
Purchase #5	$194.62	10.619%	$215.2867	$215.29	$215.30	$215.30
Purchase #6	$10.82	3.674%	$11.2175	$11.22	$11.20	$11.20
Purchase #7	$148.43	10.728%	$164.3536	$164.35	$164.35	$164.40
7 purchase totals =	$834.51		$912.4060	$912.40	$912.40	$912.40