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	$100.72	3.506%	$104.2512	$104.25	$104.25	$104.30
Purchase #2	$102.58	11.797%	$114.6814	$114.68	$114.70	$114.70
Purchase #3	$70.38	11.624%	$78.561	$78.56	$78.55	$78.60
Purchase #4	$143.80	3.537%	$148.8862	$148.89	$148.90	$148.90
Purchase #5	$101.69	3.336%	$105.0824	$105.08	$105.10	$105.10
Purchase #6	$11.39	3.805%	$11.8234	$11.82	$11.80	$11.80
Purchase #7	$86.83	11.516%	$96.8293	$96.83	$96.85	$96.80
7 purchase totals =	$617.39		$660.1149	$660.11	$660.15	$660.20