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	$153.82	5.628%	$162.477	$162.48	$162.50	$162.50
Purchase #2	$104.50	6.789%	$111.5945	$111.59	$111.60	$111.60
Purchase #3	$33.94	8.682%	$36.8867	$36.89	$36.90	$36.90
Purchase #4	$102.72	13.174%	$116.2523	$116.25	$116.25	$116.30
Purchase #5	$197.83	12.487%	$222.533	$222.53	$222.55	$222.50
Purchase #6	$72.77	11.220%	$80.9348	$80.93	$80.95	$80.90
Purchase #7	$84.42	9.495%	$92.4357	$92.44	$92.45	$92.40
7 purchase totals =	$750.00		$823.1140	$823.11	$823.20	$823.10