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	$244.71	5.581%	$258.3673	$258.37	$258.35	$258.40
Purchase #2	$180.50	10.676%	$199.7702	$199.77	$199.75	$199.80
Purchase #3	$97.32	6.689%	$103.8297	$103.83	$103.85	$103.80
Purchase #4	$18.89	13.197%	$21.3829	$21.38	$21.40	$21.40
Purchase #5	$168.80	11.642%	$188.4517	$188.45	$188.45	$188.50
Purchase #6	$73.33	8.260%	$79.3871	$79.39	$79.40	$79.40
Purchase #7	$207.38	10.699%	$229.5676	$229.57	$229.55	$229.60
7 purchase totals =	$990.93		$1,080.7565	$1,080.76	$1,080.75	$1,080.90