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	$31.36	4.340%	$32.721	$32.72	$32.70	$32.70
Purchase #2	$36.28	7.471%	$38.9905	$38.99	$39.00	$39.00
Purchase #3	$48.92	11.493%	$54.5424	$54.54	$54.55	$54.50
Purchase #4	$106.70	3.254%	$110.172	$110.17	$110.15	$110.20
Purchase #5	$104.33	7.787%	$112.4542	$112.45	$112.45	$112.50
Purchase #6	$18.25	4.286%	$19.0322	$19.03	$19.05	$19.00
Purchase #7	$98.31	11.327%	$109.4456	$109.45	$109.45	$109.40
7 purchase totals =	$444.15		$477.3579	$477.35	$477.35	$477.30