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	$71.70	10.376%	$79.1396	$79.14	$79.15	$79.10
Purchase #2	$97.46	13.733%	$110.8442	$110.84	$110.85	$110.80
Purchase #3	$40.45	5.806%	$42.7985	$42.80	$42.80	$42.80
Purchase #4	$172.36	13.788%	$196.125	$196.13	$196.15	$196.10
Purchase #5	$164.65	7.165%	$176.4472	$176.45	$176.45	$176.40
Purchase #6	$194.83	9.759%	$213.8435	$213.84	$213.85	$213.80
Purchase #7	$19.33	4.615%	$20.2221	$20.22	$20.20	$20.20
7 purchase totals =	$760.78		$839.4201	$839.42	$839.45	$839.20