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	$39.40	9.718%	$43.2289	$43.23	$43.25	$43.20
Purchase #2	$62.61	13.107%	$70.8163	$70.82	$70.80	$70.80
Purchase #3	$51.87	4.298%	$54.0994	$54.10	$54.10	$54.10
Purchase #4	$236.47	4.206%	$246.4159	$246.42	$246.40	$246.40
Purchase #5	$141.51	12.254%	$158.8506	$158.85	$158.85	$158.90
Purchase #6	$55.62	5.261%	$58.5462	$58.55	$58.55	$58.50
Purchase #7	$212.85	5.196%	$223.9097	$223.91	$223.90	$223.90
7 purchase totals =	$800.33		$855.8670	$855.88	$855.85	$855.80