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	$234.36	3.209%	$241.8806	$241.88	$241.90	$241.90
Purchase #2	$144.83	11.592%	$161.6187	$161.62	$161.60	$161.60
Purchase #3	$205.44	8.249%	$222.3867	$222.39	$222.40	$222.40
Purchase #4	$30.55	5.837%	$32.3332	$32.33	$32.35	$32.30
Purchase #5	$21.77	9.259%	$23.7857	$23.79	$23.80	$23.80
Purchase #6	$96.43	3.217%	$99.5322	$99.53	$99.55	$99.50
Purchase #7	$41.33	10.606%	$45.7135	$45.71	$45.70	$45.70
7 purchase totals =	$774.71		$827.2506	$827.25	$827.30	$827.20