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	$238.94	4.282%	$249.1714	$249.17	$249.15	$249.20
Purchase #2	$100.77	8.470%	$109.3052	$109.31	$109.30	$109.30
Purchase #3	$166.29	7.163%	$178.2014	$178.20	$178.20	$178.20
Purchase #4	$18.33	11.857%	$20.5034	$20.50	$20.50	$20.50
Purchase #5	$131.66	7.591%	$141.6543	$141.65	$141.65	$141.70
Purchase #6	$213.54	4.726%	$223.6319	$223.63	$223.65	$223.60
Purchase #7	$121.48	9.250%	$132.7169	$132.72	$132.70	$132.70
7 purchase totals =	$991.01		$1,055.1845	$1,055.18	$1,055.15	$1,055.20