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	$136.53	6.405%	$145.2747	$145.27	$145.25	$145.30
Purchase #2	$36.82	4.512%	$38.4813	$38.48	$38.50	$38.50
Purchase #3	$167.38	11.852%	$187.2179	$187.22	$187.20	$187.20
Purchase #4	$172.38	13.419%	$195.5117	$195.51	$195.50	$195.50
Purchase #5	$32.70	4.401%	$34.1391	$34.14	$34.15	$34.10
Purchase #6	$85.94	10.360%	$94.8434	$94.84	$94.85	$94.80
Purchase #7	$94.66	6.320%	$100.6425	$100.64	$100.65	$100.60
7 purchase totals =	$726.41		$796.1106	$796.10	$796.10	$796.00