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	$129.73	4.208%	$135.189	$135.19	$135.20	$135.20
Purchase #2	$168.46	3.461%	$174.2904	$174.29	$174.30	$174.30
Purchase #3	$121.88	4.585%	$127.4682	$127.47	$127.45	$127.50
Purchase #4	$89.27	3.223%	$92.1472	$92.15	$92.15	$92.10
Purchase #5	$89.49	12.336%	$100.5295	$100.53	$100.55	$100.50
Purchase #6	$126.31	11.765%	$141.1704	$141.17	$141.15	$141.20
Purchase #7	$47.88	4.509%	$50.0389	$50.04	$50.05	$50.00
7 purchase totals =	$773.02		$820.8336	$820.84	$820.85	$820.80