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	$166.34	13.661%	$189.0637	$189.06	$189.05	$189.10
Purchase #2	$32.60	13.609%	$37.0365	$37.04	$37.05	$37.00
Purchase #3	$220.80	8.199%	$238.9034	$238.90	$238.90	$238.90
Purchase #4	$117.91	11.852%	$131.8847	$131.88	$131.90	$131.90
Purchase #5	$202.45	10.851%	$224.4178	$224.42	$224.40	$224.40
Purchase #6	$48.50	3.234%	$50.0685	$50.07	$50.05	$50.10
Purchase #7	$182.58	8.719%	$198.4992	$198.50	$198.50	$198.50
7 purchase totals =	$971.18		$1,069.8738	$1,069.87	$1,069.85	$1,069.90