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	$96.85	5.712%	$102.3821	$102.38	$102.40	$102.40
Purchase #2	$146.44	4.630%	$153.2202	$153.22	$153.20	$153.20
Purchase #3	$143.79	11.198%	$159.8916	$159.89	$159.90	$159.90
Purchase #4	$249.49	10.269%	$275.1101	$275.11	$275.10	$275.10
Purchase #5	$46.98	7.354%	$50.4349	$50.43	$50.45	$50.40
Purchase #6	$204.41	5.595%	$215.8467	$215.85	$215.85	$215.80
Purchase #7	$141.54	10.656%	$156.6225	$156.62	$156.60	$156.60
7 purchase totals =	$1,029.50		$1,113.5081	$1,113.50	$1,113.50	$1,113.40