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	$193.52	3.356%	$200.0145	$200.01	$200.00	$200.00
Purchase #2	$96.81	4.122%	$100.8005	$100.80	$100.80	$100.80
Purchase #3	$96.74	9.376%	$105.8103	$105.81	$105.80	$105.80
Purchase #4	$152.64	10.449%	$168.5894	$168.59	$168.60	$168.60
Purchase #5	$127.36	11.124%	$141.5275	$141.53	$141.55	$141.50
Purchase #6	$133.90	7.486%	$143.9238	$143.92	$143.90	$143.90
Purchase #7	$123.87	7.149%	$132.7255	$132.73	$132.75	$132.70
7 purchase totals =	$924.84		$993.3915	$993.39	$993.40	$993.30