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	$50.77	6.790%	$54.2173	$54.22	$54.20	$54.20
Purchase #2	$221.30	13.268%	$250.6621	$250.66	$250.65	$250.70
Purchase #3	$55.48	6.470%	$59.0696	$59.07	$59.05	$59.10
Purchase #4	$103.42	12.147%	$115.9824	$115.98	$116.00	$116.00
Purchase #5	$227.83	9.228%	$248.8542	$248.85	$248.85	$248.90
Purchase #6	$108.57	4.824%	$113.8074	$113.81	$113.80	$113.80
Purchase #7	$151.40	3.527%	$156.7399	$156.74	$156.75	$156.70
7 purchase totals =	$918.77		$999.3329	$999.33	$999.30	$999.40