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	$5.84	8.795%	$6.3536	$6.35	$6.35	$6.40
Purchase #2	$162.94	13.475%	$184.8962	$184.90	$184.90	$184.90
Purchase #3	$66.75	9.651%	$73.192	$73.19	$73.20	$73.20
Purchase #4	$57.98	7.618%	$62.3969	$62.40	$62.40	$62.40
Purchase #5	$241.69	10.522%	$267.1206	$267.12	$267.10	$267.10
Purchase #6	$165.88	4.553%	$173.4325	$173.43	$173.45	$173.40
Purchase #7	$54.31	10.314%	$59.9115	$59.91	$59.90	$59.90
7 purchase totals =	$755.39		$827.3033	$827.30	$827.30	$827.30