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	$38.60	10.204%	$42.5387	$42.54	$42.55	$42.50
Purchase #2	$114.48	4.793%	$119.967	$119.97	$119.95	$120.00
Purchase #3	$31.27	9.424%	$34.2169	$34.22	$34.20	$34.20
Purchase #4	$98.91	12.641%	$111.4132	$111.41	$111.40	$111.40
Purchase #5	$159.29	8.556%	$172.9189	$172.92	$172.90	$172.90
Purchase #6	$94.80	12.569%	$106.7154	$106.72	$106.70	$106.70
Purchase #7	$116.53	9.159%	$127.203	$127.20	$127.20	$127.20
7 purchase totals =	$653.88		$714.9731	$714.98	$714.90	$714.90