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	$136.52	8.489%	$148.1092	$148.11	$148.10	$148.10
Purchase #2	$112.64	7.617%	$121.2198	$121.22	$121.20	$121.20
Purchase #3	$162.76	3.598%	$168.6161	$168.62	$168.60	$168.60
Purchase #4	$101.30	5.176%	$106.5433	$106.54	$106.55	$106.50
Purchase #5	$138.51	10.182%	$152.6131	$152.61	$152.60	$152.60
Purchase #6	$43.75	11.675%	$48.8578	$48.86	$48.85	$48.90
Purchase #7	$136.90	4.105%	$142.5197	$142.52	$142.50	$142.50
7 purchase totals =	$832.38		$888.4790	$888.48	$888.40	$888.40