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	$91.62	12.718%	$103.2722	$103.27	$103.25	$103.30
Purchase #2	$36.56	10.638%	$40.4493	$40.45	$40.45	$40.40
Purchase #3	$20.35	13.470%	$23.0911	$23.09	$23.10	$23.10
Purchase #4	$248.67	8.806%	$270.5679	$270.57	$270.55	$270.60
Purchase #5	$175.47	12.166%	$196.8177	$196.82	$196.80	$196.80
Purchase #6	$80.29	5.302%	$84.547	$84.55	$84.55	$84.50
Purchase #7	$45.90	6.239%	$48.7637	$48.76	$48.75	$48.80
7 purchase totals =	$698.86		$767.5089	$767.51	$767.45	$767.50