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	$249.61	12.403%	$280.5691	$280.57	$280.55	$280.60
Purchase #2	$198.25	8.700%	$215.4978	$215.50	$215.50	$215.50
Purchase #3	$179.94	6.228%	$191.1467	$191.15	$191.15	$191.10
Purchase #4	$48.69	10.132%	$53.6233	$53.62	$53.60	$53.60
Purchase #5	$127.64	5.302%	$134.4075	$134.41	$134.40	$134.40
Purchase #6	$26.82	7.739%	$28.8956	$28.90	$28.90	$28.90
Purchase #7	$238.59	12.280%	$267.8889	$267.89	$267.90	$267.90
7 purchase totals =	$1,069.54		$1,172.0289	$1,172.04	$1,172.00	$1,172.00