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	$40.65	7.146%	$43.5548	$43.55	$43.55	$43.60
Purchase #2	$144.79	5.515%	$152.7752	$152.78	$152.80	$152.80
Purchase #3	$134.62	11.828%	$150.5429	$150.54	$150.55	$150.50
Purchase #4	$68.94	13.290%	$78.1021	$78.10	$78.10	$78.10
Purchase #5	$213.61	4.384%	$222.9747	$222.97	$222.95	$223.00
Purchase #6	$70.43	6.324%	$74.884	$74.88	$74.90	$74.90
Purchase #7	$96.46	11.397%	$107.4535	$107.45	$107.45	$107.50
7 purchase totals =	$769.50		$830.2872	$830.27	$830.30	$830.40