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	$47.96	8.155%	$51.8711	$51.87	$51.85	$51.90
Purchase #2	$144.49	9.743%	$158.5677	$158.57	$158.55	$158.60
Purchase #3	$116.88	4.322%	$121.9316	$121.93	$121.95	$121.90
Purchase #4	$73.76	11.458%	$82.2114	$82.21	$82.20	$82.20
Purchase #5	$81.50	5.250%	$85.7788	$85.78	$85.80	$85.80
Purchase #6	$169.25	13.363%	$191.8669	$191.87	$191.85	$191.90
Purchase #7	$159.30	12.490%	$179.1966	$179.20	$179.20	$179.20
7 purchase totals =	$793.14		$871.4241	$871.43	$871.40	$871.50