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	$85.34	5.740%	$90.2385	$90.24	$90.25	$90.20
Purchase #2	$243.76	3.827%	$253.0887	$253.09	$253.10	$253.10
Purchase #3	$41.29	13.472%	$46.8526	$46.85	$46.85	$46.90
Purchase #4	$24.95	10.325%	$27.5261	$27.53	$27.55	$27.50
Purchase #5	$160.48	11.159%	$178.388	$178.39	$178.40	$178.40
Purchase #6	$136.59	11.176%	$151.8553	$151.86	$151.85	$151.90
Purchase #7	$227.59	5.377%	$239.8275	$239.83	$239.85	$239.80
7 purchase totals =	$920.00		$987.7767	$987.79	$987.85	$987.80