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	$226.30	9.428%	$247.6356	$247.64	$247.65	$247.60
Purchase #2	$97.48	6.362%	$103.6817	$103.68	$103.70	$103.70
Purchase #3	$74.26	8.599%	$80.6456	$80.65	$80.65	$80.60
Purchase #4	$213.30	11.407%	$237.6311	$237.63	$237.65	$237.60
Purchase #5	$78.98	13.648%	$89.7592	$89.76	$89.75	$89.80
Purchase #6	$125.93	10.682%	$139.3818	$139.38	$139.40	$139.40
Purchase #7	$186.39	7.757%	$200.8483	$200.85	$200.85	$200.80
7 purchase totals =	$1,002.64		$1,099.5833	$1,099.59	$1,099.65	$1,099.50