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	$136.85	6.521%	$145.774	$145.77	$145.75	$145.80
Purchase #2	$19.55	4.333%	$20.3971	$20.40	$20.40	$20.40
Purchase #3	$141.45	6.390%	$150.4887	$150.49	$150.50	$150.50
Purchase #4	$222.25	5.694%	$234.9049	$234.90	$234.90	$234.90
Purchase #5	$219.40	8.262%	$237.5268	$237.53	$237.55	$237.50
Purchase #6	$88.61	9.251%	$96.8073	$96.81	$96.80	$96.80
Purchase #7	$215.90	3.217%	$222.8455	$222.85	$222.85	$222.80
7 purchase totals =	$1,044.01		$1,108.7443	$1,108.75	$1,108.75	$1,108.70