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	$236.31	6.862%	$252.5256	$252.53	$252.55	$252.50
Purchase #2	$221.50	9.204%	$241.8869	$241.89	$241.90	$241.90
Purchase #3	$164.32	11.152%	$182.645	$182.65	$182.65	$182.60
Purchase #4	$120.57	4.870%	$126.4418	$126.44	$126.45	$126.40
Purchase #5	$19.73	4.519%	$20.6216	$20.62	$20.60	$20.60
Purchase #6	$118.65	7.618%	$127.6888	$127.69	$127.70	$127.70
Purchase #7	$159.74	7.438%	$171.6215	$171.62	$171.60	$171.60
7 purchase totals =	$1,040.82		$1,123.4312	$1,123.44	$1,123.45	$1,123.30