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	$83.55	8.422%	$90.5866	$90.59	$90.60	$90.60
Purchase #2	$250.34	9.260%	$273.5215	$273.52	$273.50	$273.50
Purchase #3	$81.98	8.595%	$89.0262	$89.03	$89.05	$89.00
Purchase #4	$8.59	4.116%	$8.9436	$8.94	$8.95	$8.90
Purchase #5	$227.62	10.573%	$251.6863	$251.69	$251.70	$251.70
Purchase #6	$207.56	5.108%	$218.1622	$218.16	$218.15	$218.20
Purchase #7	$88.42	13.497%	$100.354	$100.35	$100.35	$100.40
7 purchase totals =	$948.06		$1,032.2804	$1,032.28	$1,032.30	$1,032.30