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	$155.29	3.857%	$161.2795	$161.28	$161.30	$161.30
Purchase #2	$90.87	11.393%	$101.2228	$101.22	$101.20	$101.20
Purchase #3	$112.85	6.789%	$120.5114	$120.51	$120.50	$120.50
Purchase #4	$236.74	7.333%	$254.1001	$254.10	$254.10	$254.10
Purchase #5	$85.27	5.524%	$89.9803	$89.98	$90.00	$90.00
Purchase #6	$248.35	13.331%	$281.4575	$281.46	$281.45	$281.50
Purchase #7	$51.68	11.194%	$57.4651	$57.47	$57.45	$57.50
7 purchase totals =	$981.05		$1,066.0167	$1,066.02	$1,066.00	$1,066.10