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	$70.55	11.796%	$78.8721	$78.87	$78.85	$78.90
Purchase #2	$33.50	4.191%	$34.904	$34.90	$34.90	$34.90
Purchase #3	$39.89	9.139%	$43.5355	$43.54	$43.55	$43.50
Purchase #4	$160.66	12.282%	$180.3923	$180.39	$180.40	$180.40
Purchase #5	$107.60	12.845%	$121.4212	$121.42	$121.40	$121.40
Purchase #6	$142.33	12.215%	$159.7156	$159.72	$159.70	$159.70
Purchase #7	$123.52	7.143%	$132.343	$132.34	$132.35	$132.30
7 purchase totals =	$678.05		$751.1837	$751.18	$751.15	$751.10