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	$81.38	10.395%	$89.8395	$89.84	$89.85	$89.80
Purchase #2	$108.25	3.287%	$111.8082	$111.81	$111.80	$111.80
Purchase #3	$41.26	3.690%	$42.7825	$42.78	$42.80	$42.80
Purchase #4	$121.68	6.788%	$129.9396	$129.94	$129.95	$129.90
Purchase #5	$249.65	9.559%	$273.514	$273.51	$273.50	$273.50
Purchase #6	$28.82	12.285%	$32.3605	$32.36	$32.35	$32.40
Purchase #7	$143.42	11.617%	$160.0811	$160.08	$160.10	$160.10
7 purchase totals =	$774.46		$840.3254	$840.32	$840.35	$840.30