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	$192.60	12.182%	$216.0625	$216.06	$216.05	$216.10
Purchase #2	$167.97	10.598%	$185.7715	$185.77	$185.75	$185.80
Purchase #3	$179.87	10.168%	$198.1592	$198.16	$198.15	$198.20
Purchase #4	$130.48	13.635%	$148.2709	$148.27	$148.25	$148.30
Purchase #5	$52.73	9.190%	$57.5759	$57.58	$57.60	$57.60
Purchase #6	$18.71	3.369%	$19.3403	$19.34	$19.35	$19.30
Purchase #7	$82.50	10.272%	$90.9744	$90.97	$90.95	$91.00
7 purchase totals =	$824.86		$916.1547	$916.15	$916.10	$916.30