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	$167.85	6.576%	$178.8878	$178.89	$178.90	$178.90
Purchase #2	$177.83	4.143%	$185.1975	$185.20	$185.20	$185.20
Purchase #3	$54.67	13.124%	$61.8449	$61.84	$61.85	$61.80
Purchase #4	$99.69	4.277%	$103.9537	$103.95	$103.95	$104.00
Purchase #5	$163.80	10.177%	$180.4699	$180.47	$180.45	$180.50
Purchase #6	$155.51	6.340%	$165.3693	$165.37	$165.35	$165.40
Purchase #7	$188.48	12.748%	$212.5074	$212.51	$212.50	$212.50
7 purchase totals =	$1,007.83		$1,088.2305	$1,088.23	$1,088.20	$1,088.30