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	$82.40	9.243%	$90.0162	$90.02	$90.00	$90.00
Purchase #2	$100.53	13.674%	$114.2765	$114.28	$114.30	$114.30
Purchase #3	$47.78	8.424%	$51.805	$51.81	$51.80	$51.80
Purchase #4	$40.66	5.675%	$42.9675	$42.97	$42.95	$43.00
Purchase #5	$234.40	4.160%	$244.151	$244.15	$244.15	$244.20
Purchase #6	$74.83	8.661%	$81.311	$81.31	$81.30	$81.30
Purchase #7	$39.52	3.239%	$40.8001	$40.80	$40.80	$40.80
7 purchase totals =	$620.12		$665.3273	$665.34	$665.30	$665.40