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	$242.28	3.796%	$251.4769	$251.48	$251.50	$251.50
Purchase #2	$120.51	6.715%	$128.6022	$128.60	$128.60	$128.60
Purchase #3	$81.74	10.205%	$90.0816	$90.08	$90.10	$90.10
Purchase #4	$35.64	8.473%	$38.6598	$38.66	$38.65	$38.70
Purchase #5	$221.42	12.857%	$249.888	$249.89	$249.90	$249.90
Purchase #6	$75.92	12.671%	$85.5398	$85.54	$85.55	$85.50
Purchase #7	$63.52	9.584%	$69.6078	$69.61	$69.60	$69.60
7 purchase totals =	$841.03		$913.8561	$913.86	$913.90	$913.90