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	$164.81	4.717%	$172.5841	$172.58	$172.60	$172.60
Purchase #2	$75.31	3.660%	$78.0663	$78.07	$78.05	$78.10
Purchase #3	$120.89	8.366%	$131.0037	$131.00	$131.00	$131.00
Purchase #4	$188.68	7.613%	$203.0442	$203.04	$203.05	$203.00
Purchase #5	$65.77	10.311%	$72.5515	$72.55	$72.55	$72.60
Purchase #6	$240.57	9.758%	$264.0448	$264.04	$264.05	$264.00
Purchase #7	$161.75	10.647%	$178.9715	$178.97	$178.95	$179.00
7 purchase totals =	$1,017.78		$1,100.2661	$1,100.25	$1,100.25	$1,100.30