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	$245.69	5.664%	$259.6059	$259.61	$259.60	$259.60
Purchase #2	$237.67	13.441%	$269.6152	$269.62	$269.60	$269.60
Purchase #3	$18.91	8.223%	$20.465	$20.47	$20.45	$20.50
Purchase #4	$117.45	8.336%	$127.2406	$127.24	$127.25	$127.20
Purchase #5	$162.86	9.494%	$178.3219	$178.32	$178.30	$178.30
Purchase #6	$166.91	13.330%	$189.1591	$189.16	$189.15	$189.20
Purchase #7	$205.88	7.854%	$222.0498	$222.05	$222.05	$222.00
7 purchase totals =	$1,155.37		$1,266.4575	$1,266.47	$1,266.40	$1,266.40