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	$30.98	6.477%	$32.9866	$32.99	$33.00	$33.00
Purchase #2	$201.41	12.259%	$226.1009	$226.10	$226.10	$226.10
Purchase #3	$90.82	8.513%	$98.5515	$98.55	$98.55	$98.60
Purchase #4	$71.88	9.105%	$78.4247	$78.42	$78.40	$78.40
Purchase #5	$31.33	4.103%	$32.6155	$32.62	$32.60	$32.60
Purchase #6	$223.28	11.661%	$249.3167	$249.32	$249.30	$249.30
Purchase #7	$238.28	10.212%	$262.6132	$262.61	$262.60	$262.60
7 purchase totals =	$887.98		$980.6091	$980.61	$980.55	$980.60