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	$41.41	6.278%	$44.0097	$44.01	$44.00	$44.00
Purchase #2	$99.50	6.459%	$105.9267	$105.93	$105.95	$105.90
Purchase #3	$84.89	10.557%	$93.8518	$93.85	$93.85	$93.90
Purchase #4	$124.28	13.684%	$141.2865	$141.29	$141.30	$141.30
Purchase #5	$103.51	12.126%	$116.0616	$116.06	$116.05	$116.10
Purchase #6	$165.86	7.641%	$178.5334	$178.53	$178.55	$178.50
Purchase #7	$121.41	4.665%	$127.0738	$127.07	$127.05	$127.10
7 purchase totals =	$740.86		$806.7435	$806.74	$806.75	$806.80