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	$181.88	3.536%	$188.3113	$188.31	$188.30	$188.30
Purchase #2	$224.90	13.578%	$255.4369	$255.44	$255.45	$255.40
Purchase #3	$112.48	6.370%	$119.645	$119.65	$119.65	$119.60
Purchase #4	$53.46	6.735%	$57.0605	$57.06	$57.05	$57.10
Purchase #5	$195.59	4.786%	$204.9509	$204.95	$204.95	$205.00
Purchase #6	$140.42	10.404%	$155.0293	$155.03	$155.05	$155.00
Purchase #7	$18.35	13.708%	$20.8654	$20.87	$20.85	$20.90
7 purchase totals =	$927.08		$1,001.2993	$1,001.31	$1,001.30	$1,001.30