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	$49.96	13.463%	$56.6861	$56.69	$56.70	$56.70
Purchase #2	$102.41	8.626%	$111.2439	$111.24	$111.25	$111.20
Purchase #3	$181.88	4.387%	$189.8591	$189.86	$189.85	$189.90
Purchase #4	$220.97	3.345%	$228.3614	$228.36	$228.35	$228.40
Purchase #5	$245.25	5.767%	$259.3936	$259.39	$259.40	$259.40
Purchase #6	$105.42	8.275%	$114.1435	$114.14	$114.15	$114.10
Purchase #7	$123.42	11.341%	$137.4171	$137.42	$137.40	$137.40
7 purchase totals =	$1,029.31		$1,097.1047	$1,097.10	$1,097.10	$1,097.10