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	$227.62	4.657%	$238.2203	$238.22	$238.20	$238.20
Purchase #2	$220.55	13.779%	$250.9396	$250.94	$250.95	$250.90
Purchase #3	$227.99	11.530%	$254.2772	$254.28	$254.30	$254.30
Purchase #4	$178.33	9.429%	$195.1447	$195.14	$195.15	$195.10
Purchase #5	$108.64	13.610%	$123.4259	$123.43	$123.45	$123.40
Purchase #6	$7.89	12.531%	$8.8787	$8.88	$8.90	$8.90
Purchase #7	$88.27	13.737%	$100.3956	$100.40	$100.40	$100.40
7 purchase totals =	$1,059.29		$1,171.2820	$1,171.29	$1,171.35	$1,171.20