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	$68.77	3.124%	$70.9184	$70.92	$70.90	$70.90
Purchase #2	$137.82	13.801%	$156.8405	$156.84	$156.85	$156.80
Purchase #3	$51.49	4.545%	$53.8302	$53.83	$53.85	$53.80
Purchase #4	$155.96	12.391%	$175.285	$175.29	$175.30	$175.30
Purchase #5	$231.87	13.503%	$263.1794	$263.18	$263.20	$263.20
Purchase #6	$73.65	12.130%	$82.5837	$82.58	$82.60	$82.60
Purchase #7	$115.51	3.363%	$119.3946	$119.39	$119.40	$119.40
7 purchase totals =	$835.07		$922.0318	$922.03	$922.10	$922.00