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	$224.73	6.189%	$238.6385	$238.64	$238.65	$238.60
Purchase #2	$240.96	7.440%	$258.8874	$258.89	$258.90	$258.90
Purchase #3	$215.60	11.466%	$240.3207	$240.32	$240.30	$240.30
Purchase #4	$217.87	5.244%	$229.2951	$229.30	$229.30	$229.30
Purchase #5	$135.44	6.854%	$144.7231	$144.72	$144.70	$144.70
Purchase #6	$52.48	12.707%	$59.1486	$59.15	$59.15	$59.10
Purchase #7	$221.74	13.257%	$251.1361	$251.14	$251.15	$251.10
7 purchase totals =	$1,308.82		$1,422.1495	$1,422.16	$1,422.15	$1,422.00