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	$90.39	11.286%	$100.5914	$100.59	$100.60	$100.60
Purchase #2	$163.90	5.377%	$172.7129	$172.71	$172.70	$172.70
Purchase #3	$175.88	5.125%	$184.8939	$184.89	$184.90	$184.90
Purchase #4	$118.28	4.833%	$123.9965	$124.00	$124.00	$124.00
Purchase #5	$106.83	12.778%	$120.4807	$120.48	$120.50	$120.50
Purchase #6	$221.51	12.860%	$249.9962	$250.00	$250.00	$250.00
Purchase #7	$232.59	3.353%	$240.3887	$240.39	$240.40	$240.40
7 purchase totals =	$1,109.38		$1,193.0603	$1,193.06	$1,193.10	$1,193.10