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	$173.88	7.471%	$186.8706	$186.87	$186.85	$186.90
Purchase #2	$94.25	7.526%	$101.3433	$101.34	$101.35	$101.30
Purchase #3	$139.59	13.790%	$158.8395	$158.84	$158.85	$158.80
Purchase #4	$139.39	3.388%	$144.1125	$144.11	$144.10	$144.10
Purchase #5	$234.44	8.440%	$254.2267	$254.23	$254.25	$254.20
Purchase #6	$102.83	5.446%	$108.4301	$108.43	$108.45	$108.40
Purchase #7	$109.39	12.568%	$123.1381	$123.14	$123.15	$123.10
7 purchase totals =	$993.77		$1,076.9608	$1,076.96	$1,077.00	$1,076.80