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	$160.97	3.455%	$166.5315	$166.53	$166.55	$166.50
Purchase #2	$88.98	11.730%	$99.4174	$99.42	$99.40	$99.40
Purchase #3	$58.41	10.800%	$64.7183	$64.72	$64.70	$64.70
Purchase #4	$135.60	10.637%	$150.0238	$150.02	$150.00	$150.00
Purchase #5	$208.76	3.610%	$216.2962	$216.30	$216.30	$216.30
Purchase #6	$145.40	3.748%	$150.8496	$150.85	$150.85	$150.80
Purchase #7	$66.86	7.824%	$72.0911	$72.09	$72.10	$72.10
7 purchase totals =	$864.98		$919.9279	$919.93	$919.90	$919.80