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	$49.85	8.153%	$53.9143	$53.91	$53.90	$53.90
Purchase #2	$240.85	5.594%	$254.3231	$254.32	$254.30	$254.30
Purchase #3	$42.93	13.426%	$48.6938	$48.69	$48.70	$48.70
Purchase #4	$127.42	10.263%	$140.4971	$140.50	$140.50	$140.50
Purchase #5	$131.87	6.826%	$140.8714	$140.87	$140.85	$140.90
Purchase #6	$20.38	3.409%	$21.0748	$21.07	$21.05	$21.10
Purchase #7	$179.50	10.547%	$198.4319	$198.43	$198.45	$198.40
7 purchase totals =	$792.80		$857.8064	$857.79	$857.75	$857.80