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	$26.86	9.844%	$29.5041	$29.50	$29.50	$29.50
Purchase #2	$207.54	11.323%	$231.0398	$231.04	$231.05	$231.00
Purchase #3	$194.67	10.613%	$215.3303	$215.33	$215.35	$215.30
Purchase #4	$150.42	11.376%	$167.5318	$167.53	$167.55	$167.50
Purchase #5	$165.92	13.735%	$188.7091	$188.71	$188.70	$188.70
Purchase #6	$92.72	12.507%	$104.3165	$104.32	$104.30	$104.30
Purchase #7	$76.78	5.282%	$80.8355	$80.84	$80.85	$80.80
7 purchase totals =	$914.91		$1,017.2671	$1,017.27	$1,017.30	$1,017.10