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	$229.61	12.145%	$257.4961	$257.50	$257.50	$257.50
Purchase #2	$59.28	6.398%	$63.0727	$63.07	$63.05	$63.10
Purchase #3	$124.43	11.842%	$139.165	$139.17	$139.15	$139.20
Purchase #4	$67.89	4.356%	$70.8473	$70.85	$70.85	$70.80
Purchase #5	$110.47	3.262%	$114.0735	$114.07	$114.05	$114.10
Purchase #6	$35.55	5.834%	$37.624	$37.62	$37.60	$37.60
Purchase #7	$28.47	10.679%	$31.5103	$31.51	$31.50	$31.50
7 purchase totals =	$655.70		$713.7889	$713.79	$713.70	$713.80