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	$99.61	10.307%	$109.8768	$109.88	$109.90	$109.90
Purchase #2	$66.85	8.846%	$72.7636	$72.76	$72.75	$72.80
Purchase #3	$236.55	13.348%	$268.1247	$268.12	$268.10	$268.10
Purchase #4	$241.38	9.812%	$265.0642	$265.06	$265.05	$265.10
Purchase #5	$107.67	3.383%	$111.3125	$111.31	$111.30	$111.30
Purchase #6	$77.66	4.406%	$81.0817	$81.08	$81.10	$81.10
Purchase #7	$181.84	4.355%	$189.7591	$189.76	$189.75	$189.80
7 purchase totals =	$1,011.56		$1,097.9826	$1,097.97	$1,097.95	$1,098.10