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	$99.60	3.857%	$103.4416	$103.44	$103.45	$103.40
Purchase #2	$236.71	9.794%	$259.8934	$259.89	$259.90	$259.90
Purchase #3	$20.80	6.845%	$22.2238	$22.22	$22.20	$22.20
Purchase #4	$28.60	11.340%	$31.8432	$31.84	$31.85	$31.80
Purchase #5	$172.62	6.307%	$183.5071	$183.51	$183.50	$183.50
Purchase #6	$71.31	13.440%	$80.8941	$80.89	$80.90	$80.90
Purchase #7	$223.97	10.606%	$247.7243	$247.72	$247.70	$247.70
7 purchase totals =	$853.61		$929.5275	$929.51	$929.50	$929.40