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	$109.31	7.541%	$117.5531	$117.55	$117.55	$117.60
Purchase #2	$78.83	7.344%	$84.6193	$84.62	$84.60	$84.60
Purchase #3	$108.75	13.679%	$123.6259	$123.63	$123.65	$123.60
Purchase #4	$107.44	4.197%	$111.9493	$111.95	$111.95	$111.90
Purchase #5	$185.32	13.650%	$210.6162	$210.62	$210.60	$210.60
Purchase #6	$189.43	9.335%	$207.1133	$207.11	$207.10	$207.10
Purchase #7	$134.80	5.258%	$141.8878	$141.89	$141.90	$141.90
7 purchase totals =	$913.88		$997.3649	$997.37	$997.35	$997.30