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	$120.81	5.400%	$127.3337	$127.33	$127.35	$127.30
Purchase #2	$89.50	13.242%	$101.3516	$101.35	$101.35	$101.40
Purchase #3	$194.89	13.655%	$221.5022	$221.50	$221.50	$221.50
Purchase #4	$23.75	3.174%	$24.5038	$24.50	$24.50	$24.50
Purchase #5	$29.96	11.656%	$33.4521	$33.45	$33.45	$33.50
Purchase #6	$195.31	13.447%	$221.5733	$221.57	$221.55	$221.60
Purchase #7	$210.29	11.862%	$235.2346	$235.23	$235.25	$235.20
7 purchase totals =	$864.51		$964.9513	$964.93	$964.95	$965.00