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	$19.98	7.609%	$21.5003	$21.50	$21.50	$21.50
Purchase #2	$78.46	4.591%	$82.0621	$82.06	$82.05	$82.10
Purchase #3	$83.51	7.829%	$90.048	$90.05	$90.05	$90.00
Purchase #4	$222.66	6.336%	$236.7677	$236.77	$236.75	$236.80
Purchase #5	$207.26	4.723%	$217.0489	$217.05	$217.05	$217.00
Purchase #6	$116.82	6.594%	$124.5231	$124.52	$124.50	$124.50
Purchase #7	$172.90	4.178%	$180.1238	$180.12	$180.10	$180.10
7 purchase totals =	$901.59		$952.0739	$952.07	$952.00	$952.00