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	$227.76	10.343%	$251.3172	$251.32	$251.30	$251.30
Purchase #2	$164.64	7.222%	$176.5303	$176.53	$176.55	$176.50
Purchase #3	$96.42	4.353%	$100.6172	$100.62	$100.60	$100.60
Purchase #4	$49.72	11.410%	$55.3931	$55.39	$55.40	$55.40
Purchase #5	$209.65	4.625%	$219.3463	$219.35	$219.35	$219.30
Purchase #6	$75.42	5.447%	$79.5281	$79.53	$79.55	$79.50
Purchase #7	$103.90	12.182%	$116.5571	$116.56	$116.55	$116.60
7 purchase totals =	$927.51		$999.2893	$999.30	$999.30	$999.20