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	$95.41	13.589%	$108.3753	$108.38	$108.40	$108.40
Purchase #2	$89.96	8.625%	$97.7191	$97.72	$97.70	$97.70
Purchase #3	$235.47	7.391%	$252.8736	$252.87	$252.85	$252.90
Purchase #4	$35.58	7.132%	$38.1176	$38.12	$38.10	$38.10
Purchase #5	$65.94	8.592%	$71.6056	$71.61	$71.60	$71.60
Purchase #6	$141.69	9.660%	$155.3773	$155.38	$155.40	$155.40
Purchase #7	$94.73	11.328%	$105.461	$105.46	$105.45	$105.50
7 purchase totals =	$758.78		$829.5295	$829.54	$829.50	$829.60