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	$133.80	11.310%	$148.9328	$148.93	$148.95	$148.90
Purchase #2	$81.53	11.256%	$90.707	$90.71	$90.70	$90.70
Purchase #3	$139.97	9.581%	$153.3805	$153.38	$153.40	$153.40
Purchase #4	$82.62	11.521%	$92.1387	$92.14	$92.15	$92.10
Purchase #5	$200.83	7.322%	$215.5348	$215.53	$215.55	$215.50
Purchase #6	$90.83	3.598%	$94.0981	$94.10	$94.10	$94.10
Purchase #7	$42.32	7.790%	$45.6167	$45.62	$45.60	$45.60
7 purchase totals =	$771.90		$840.4086	$840.41	$840.45	$840.30