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	$160.92	4.724%	$168.5219	$168.52	$168.50	$168.50
Purchase #2	$90.94	11.399%	$101.3063	$101.31	$101.30	$101.30
Purchase #3	$115.32	3.304%	$119.1302	$119.13	$119.15	$119.10
Purchase #4	$106.27	12.858%	$119.9342	$119.93	$119.95	$119.90
Purchase #5	$237.50	5.282%	$250.0448	$250.04	$250.05	$250.00
Purchase #6	$194.26	5.441%	$204.8297	$204.83	$204.85	$204.80
Purchase #7	$95.59	9.780%	$104.9387	$104.94	$104.95	$104.90
7 purchase totals =	$1,000.80		$1,068.7058	$1,068.70	$1,068.75	$1,068.50