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	$28.31	5.813%	$29.9557	$29.96	$29.95	$30.00
Purchase #2	$184.36	11.639%	$205.8177	$205.82	$205.80	$205.80
Purchase #3	$215.31	13.868%	$245.1692	$245.17	$245.15	$245.20
Purchase #4	$126.87	12.687%	$142.966	$142.97	$142.95	$143.00
Purchase #5	$54.46	12.693%	$61.3726	$61.37	$61.35	$61.40
Purchase #6	$223.38	12.510%	$251.3248	$251.32	$251.30	$251.30
Purchase #7	$134.35	10.458%	$148.4003	$148.40	$148.40	$148.40
7 purchase totals =	$967.04		$1,085.0063	$1,085.01	$1,084.90	$1,085.10