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	$77.31	4.253%	$80.598	$80.60	$80.60	$80.60
Purchase #2	$245.60	11.339%	$273.4486	$273.45	$273.45	$273.40
Purchase #3	$103.56	5.794%	$109.5603	$109.56	$109.55	$109.60
Purchase #4	$66.62	10.153%	$73.3839	$73.38	$73.40	$73.40
Purchase #5	$65.49	11.221%	$72.8386	$72.84	$72.85	$72.80
Purchase #6	$97.64	7.141%	$104.6125	$104.61	$104.60	$104.60
Purchase #7	$187.98	4.666%	$196.7511	$196.75	$196.75	$196.80
7 purchase totals =	$844.20		$911.1930	$911.19	$911.20	$911.20