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	$29.73	5.782%	$31.449	$31.45	$31.45	$31.40
Purchase #2	$157.76	6.823%	$168.524	$168.52	$168.50	$168.50
Purchase #3	$42.62	9.553%	$46.6915	$46.69	$46.70	$46.70
Purchase #4	$225.68	7.398%	$242.3758	$242.38	$242.40	$242.40
Purchase #5	$102.54	6.383%	$109.0851	$109.09	$109.10	$109.10
Purchase #6	$152.34	3.701%	$157.9781	$157.98	$158.00	$158.00
Purchase #7	$65.85	9.570%	$72.1518	$72.15	$72.15	$72.20
7 purchase totals =	$776.52		$828.2553	$828.26	$828.30	$828.30