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	$18.57	10.785%	$20.5728	$20.57	$20.55	$20.60
Purchase #2	$95.53	12.583%	$107.5505	$107.55	$107.55	$107.60
Purchase #3	$77.53	10.291%	$85.5086	$85.51	$85.50	$85.50
Purchase #4	$225.65	5.600%	$238.2864	$238.29	$238.30	$238.30
Purchase #5	$188.72	5.692%	$199.4619	$199.46	$199.45	$199.50
Purchase #6	$141.73	6.582%	$151.0587	$151.06	$151.05	$151.10
Purchase #7	$5.66	9.866%	$6.2184	$6.22	$6.20	$6.20
7 purchase totals =	$753.39		$808.6573	$808.66	$808.60	$808.80