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	$121.35	8.184%	$131.2813	$131.28	$131.30	$131.30
Purchase #2	$173.94	5.524%	$183.5484	$183.55	$183.55	$183.50
Purchase #3	$151.29	12.733%	$170.5538	$170.55	$170.55	$170.60
Purchase #4	$144.59	4.693%	$151.3756	$151.38	$151.40	$151.40
Purchase #5	$131.48	11.719%	$146.8881	$146.89	$146.90	$146.90
Purchase #6	$177.50	3.127%	$183.0504	$183.05	$183.05	$183.10
Purchase #7	$179.36	3.280%	$185.243	$185.24	$185.25	$185.20
7 purchase totals =	$1,079.51		$1,151.9406	$1,151.94	$1,152.00	$1,152.00