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	$99.98	4.412%	$104.3911	$104.39	$104.40	$104.40
Purchase #2	$153.50	9.742%	$168.454	$168.45	$168.45	$168.50
Purchase #3	$87.56	13.463%	$99.3482	$99.35	$99.35	$99.30
Purchase #4	$70.89	9.322%	$77.4984	$77.50	$77.50	$77.50
Purchase #5	$54.27	5.197%	$57.0904	$57.09	$57.10	$57.10
Purchase #6	$5.77	4.597%	$6.0352	$6.04	$6.05	$6.00
Purchase #7	$221.71	8.769%	$241.1517	$241.15	$241.15	$241.20
7 purchase totals =	$693.68		$753.9690	$753.97	$754.00	$754.00