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	$138.96	5.776%	$146.9863	$146.99	$147.00	$147.00
Purchase #2	$29.52	9.111%	$32.2096	$32.21	$32.20	$32.20
Purchase #3	$92.90	8.298%	$100.6088	$100.61	$100.60	$100.60
Purchase #4	$21.41	9.497%	$23.4433	$23.44	$23.45	$23.40
Purchase #5	$211.91	7.550%	$227.9092	$227.91	$227.90	$227.90
Purchase #6	$131.59	3.840%	$136.6431	$136.64	$136.65	$136.60
Purchase #7	$110.60	11.837%	$123.6917	$123.69	$123.70	$123.70
7 purchase totals =	$736.89		$791.4920	$791.49	$791.50	$791.40