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	$27.88	8.584%	$30.2732	$30.27	$30.25	$30.30
Purchase #2	$56.28	9.105%	$61.4043	$61.40	$61.40	$61.40
Purchase #3	$187.75	4.517%	$196.2307	$196.23	$196.25	$196.20
Purchase #4	$156.39	3.813%	$162.3532	$162.35	$162.35	$162.40
Purchase #5	$198.26	13.224%	$224.4779	$224.48	$224.50	$224.50
Purchase #6	$128.27	6.612%	$136.7512	$136.75	$136.75	$136.80
Purchase #7	$95.79	3.680%	$99.3151	$99.32	$99.30	$99.30
7 purchase totals =	$850.62		$910.8056	$910.80	$910.80	$910.90