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	$237.41	13.664%	$269.8497	$269.85	$269.85	$269.80
Purchase #2	$99.74	3.589%	$103.3197	$103.32	$103.30	$103.30
Purchase #3	$89.60	8.403%	$97.1291	$97.13	$97.15	$97.10
Purchase #4	$233.32	8.689%	$253.5932	$253.59	$253.60	$253.60
Purchase #5	$13.29	10.701%	$14.7122	$14.71	$14.70	$14.70
Purchase #6	$208.50	8.287%	$225.7784	$225.78	$225.80	$225.80
Purchase #7	$51.72	8.449%	$56.0898	$56.09	$56.10	$56.10
7 purchase totals =	$933.58		$1,020.4721	$1,020.47	$1,020.50	$1,020.40