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	$36.32	7.523%	$39.0524	$39.05	$39.05	$39.10
Purchase #2	$127.43	11.640%	$142.2629	$142.26	$142.25	$142.30
Purchase #3	$61.30	8.281%	$66.3763	$66.38	$66.40	$66.40
Purchase #4	$65.60	9.163%	$71.6109	$71.61	$71.60	$71.60
Purchase #5	$203.33	5.771%	$215.0642	$215.06	$215.05	$215.10
Purchase #6	$236.85	11.399%	$263.8485	$263.85	$263.85	$263.80
Purchase #7	$221.38	9.203%	$241.7536	$241.75	$241.75	$241.80
7 purchase totals =	$952.21		$1,039.9688	$1,039.96	$1,039.95	$1,040.10