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	$100.27	9.588%	$109.8839	$109.88	$109.90	$109.90
Purchase #2	$215.77	4.192%	$224.8151	$224.82	$224.80	$224.80
Purchase #3	$122.38	9.849%	$134.4332	$134.43	$134.45	$134.40
Purchase #4	$134.62	6.512%	$143.3865	$143.39	$143.40	$143.40
Purchase #5	$243.92	11.431%	$271.8025	$271.80	$271.80	$271.80
Purchase #6	$5.62	7.687%	$6.052	$6.05	$6.05	$6.10
Purchase #7	$117.28	9.797%	$128.7699	$128.77	$128.75	$128.80
7 purchase totals =	$939.86		$1,019.1431	$1,019.14	$1,019.15	$1,019.20