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	$229.32	11.320%	$255.279	$255.28	$255.30	$255.30
Purchase #2	$150.84	6.534%	$160.6959	$160.70	$160.70	$160.70
Purchase #3	$229.58	3.194%	$236.9128	$236.91	$236.90	$236.90
Purchase #4	$101.64	6.686%	$108.4357	$108.44	$108.45	$108.40
Purchase #5	$184.53	13.119%	$208.7385	$208.74	$208.75	$208.70
Purchase #6	$118.40	4.352%	$123.5528	$123.55	$123.55	$123.60
Purchase #7	$142.84	13.772%	$162.5119	$162.51	$162.50	$162.50
7 purchase totals =	$1,157.15		$1,256.1266	$1,256.13	$1,256.15	$1,256.10