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	$172.40	8.816%	$187.5988	$187.60	$187.60	$187.60
Purchase #2	$204.72	10.314%	$225.8348	$225.83	$225.85	$225.80
Purchase #3	$99.42	3.515%	$102.9146	$102.91	$102.90	$102.90
Purchase #4	$89.48	6.452%	$95.2532	$95.25	$95.25	$95.30
Purchase #5	$56.90	7.719%	$61.2921	$61.29	$61.30	$61.30
Purchase #6	$32.73	10.679%	$36.2252	$36.23	$36.25	$36.20
Purchase #7	$143.31	12.314%	$160.9572	$160.96	$160.95	$161.00
7 purchase totals =	$798.96		$870.0759	$870.07	$870.10	$870.10