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	$191.73	13.412%	$217.4448	$217.44	$217.45	$217.40
Purchase #2	$145.87	9.356%	$159.5176	$159.52	$159.50	$159.50
Purchase #3	$200.79	10.155%	$221.1802	$221.18	$221.20	$221.20
Purchase #4	$14.90	4.574%	$15.5815	$15.58	$15.60	$15.60
Purchase #5	$160.98	6.282%	$171.0928	$171.09	$171.10	$171.10
Purchase #6	$72.74	7.573%	$78.2486	$78.25	$78.25	$78.20
Purchase #7	$100.82	12.835%	$113.7602	$113.76	$113.75	$113.80
7 purchase totals =	$887.83		$976.8257	$976.82	$976.85	$976.80