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	$239.74	7.501%	$257.7229	$257.72	$257.70	$257.70
Purchase #2	$244.60	12.786%	$275.8746	$275.87	$275.85	$275.90
Purchase #3	$156.32	12.856%	$176.4165	$176.42	$176.40	$176.40
Purchase #4	$120.85	13.373%	$137.0113	$137.01	$137.00	$137.00
Purchase #5	$85.47	12.211%	$95.9067	$95.91	$95.90	$95.90
Purchase #6	$71.67	12.333%	$80.5091	$80.51	$80.50	$80.50
Purchase #7	$53.69	3.175%	$55.3947	$55.39	$55.40	$55.40
7 purchase totals =	$972.34		$1,078.8358	$1,078.83	$1,078.75	$1,078.80