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	$89.39	12.773%	$100.8078	$100.81	$100.80	$100.80
Purchase #2	$37.72	7.346%	$40.4909	$40.49	$40.50	$40.50
Purchase #3	$172.67	4.478%	$180.4022	$180.40	$180.40	$180.40
Purchase #4	$200.70	9.575%	$219.917	$219.92	$219.90	$219.90
Purchase #5	$148.58	12.120%	$166.5879	$166.59	$166.60	$166.60
Purchase #6	$23.87	13.344%	$27.0552	$27.06	$27.05	$27.10
Purchase #7	$16.93	6.692%	$18.063	$18.06	$18.05	$18.10
7 purchase totals =	$689.86		$753.3240	$753.33	$753.30	$753.40