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	$6.74	11.588%	$7.521	$7.52	$7.50	$7.50
Purchase #2	$176.63	8.305%	$191.2991	$191.30	$191.30	$191.30
Purchase #3	$208.89	13.800%	$237.7168	$237.72	$237.70	$237.70
Purchase #4	$166.92	10.521%	$184.4817	$184.48	$184.50	$184.50
Purchase #5	$71.39	13.273%	$80.8656	$80.87	$80.85	$80.90
Purchase #6	$226.69	4.496%	$236.882	$236.88	$236.90	$236.90
Purchase #7	$80.89	5.611%	$85.4287	$85.43	$85.45	$85.40
7 purchase totals =	$938.15		$1,024.1949	$1,024.20	$1,024.20	$1,024.20