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	$33.60	11.696%	$37.5299	$37.53	$37.55	$37.50
Purchase #2	$150.45	3.449%	$155.639	$155.64	$155.65	$155.60
Purchase #3	$207.86	7.632%	$223.7239	$223.72	$223.70	$223.70
Purchase #4	$135.89	5.247%	$143.0201	$143.02	$143.00	$143.00
Purchase #5	$144.75	8.255%	$156.6991	$156.70	$156.70	$156.70
Purchase #6	$176.63	6.494%	$188.1004	$188.10	$188.10	$188.10
Purchase #7	$162.54	8.703%	$176.6859	$176.69	$176.70	$176.70
7 purchase totals =	$1,011.72		$1,081.3983	$1,081.40	$1,081.40	$1,081.30