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	$36.87	10.141%	$40.609	$40.61	$40.60	$40.60
Purchase #2	$183.62	7.186%	$196.8149	$196.81	$196.80	$196.80
Purchase #3	$72.87	7.370%	$78.2405	$78.24	$78.25	$78.20
Purchase #4	$126.52	10.290%	$139.5389	$139.54	$139.55	$139.50
Purchase #5	$169.74	6.159%	$180.1943	$180.19	$180.20	$180.20
Purchase #6	$122.52	3.458%	$126.7567	$126.76	$126.75	$126.80
Purchase #7	$236.32	13.272%	$267.6844	$267.68	$267.70	$267.70
7 purchase totals =	$948.46		$1,029.8387	$1,029.83	$1,029.85	$1,029.80