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	$30.61	9.307%	$33.4589	$33.46	$33.45	$33.50
Purchase #2	$165.93	12.832%	$187.2221	$187.22	$187.20	$187.20
Purchase #3	$37.91	4.807%	$39.7323	$39.73	$39.75	$39.70
Purchase #4	$103.81	11.789%	$116.0482	$116.05	$116.05	$116.00
Purchase #5	$172.32	7.598%	$185.4129	$185.41	$185.40	$185.40
Purchase #6	$102.35	13.397%	$116.0618	$116.06	$116.05	$116.10
Purchase #7	$7.82	8.522%	$8.4864	$8.49	$8.50	$8.50
7 purchase totals =	$620.75		$686.4226	$686.42	$686.40	$686.40