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	$90.31	11.126%	$100.3579	$100.36	$100.35	$100.40
Purchase #2	$77.52	10.712%	$85.8239	$85.82	$85.80	$85.80
Purchase #3	$198.68	3.813%	$206.2557	$206.26	$206.25	$206.30
Purchase #4	$166.82	6.256%	$177.2563	$177.26	$177.25	$177.30
Purchase #5	$91.95	13.722%	$104.5674	$104.57	$104.55	$104.60
Purchase #6	$81.55	11.293%	$90.7594	$90.76	$90.75	$90.80
Purchase #7	$217.78	13.459%	$247.091	$247.09	$247.10	$247.10
7 purchase totals =	$924.61		$1,012.1116	$1,012.12	$1,012.05	$1,012.30