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	$136.51	13.218%	$154.5539	$154.55	$154.55	$154.60
Purchase #2	$92.50	5.522%	$97.6079	$97.61	$97.60	$97.60
Purchase #3	$156.44	7.477%	$168.137	$168.14	$168.15	$168.10
Purchase #4	$115.74	12.506%	$130.2144	$130.21	$130.20	$130.20
Purchase #5	$69.61	12.599%	$78.3802	$78.38	$78.40	$78.40
Purchase #6	$30.90	11.120%	$34.3361	$34.34	$34.35	$34.30
Purchase #7	$119.75	6.178%	$127.1482	$127.15	$127.15	$127.10
7 purchase totals =	$721.45		$790.3777	$790.38	$790.40	$790.30