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	$24.82	13.735%	$28.229	$28.23	$28.25	$28.20
Purchase #2	$156.72	9.694%	$171.9124	$171.91	$171.90	$171.90
Purchase #3	$18.69	3.548%	$19.3531	$19.35	$19.35	$19.40
Purchase #4	$97.48	5.721%	$103.0568	$103.06	$103.05	$103.10
Purchase #5	$171.72	12.752%	$193.6177	$193.62	$193.60	$193.60
Purchase #6	$237.25	9.527%	$259.8528	$259.85	$259.85	$259.90
Purchase #7	$224.46	7.445%	$241.171	$241.17	$241.15	$241.20
7 purchase totals =	$931.14		$1,017.1928	$1,017.19	$1,017.15	$1,017.30