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	$5.80	8.869%	$6.3144	$6.31	$6.30	$6.30
Purchase #2	$205.47	4.859%	$215.4538	$215.45	$215.45	$215.50
Purchase #3	$74.65	8.212%	$80.7803	$80.78	$80.80	$80.80
Purchase #4	$104.39	6.857%	$111.548	$111.55	$111.55	$111.50
Purchase #5	$220.96	10.581%	$244.3398	$244.34	$244.35	$244.30
Purchase #6	$238.77	9.340%	$261.0711	$261.07	$261.05	$261.10
Purchase #7	$77.43	7.530%	$83.2605	$83.26	$83.25	$83.30
7 purchase totals =	$927.47		$1,002.7679	$1,002.76	$1,002.75	$1,002.80