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	$187.65	12.697%	$211.4759	$211.48	$211.50	$211.50
Purchase #2	$102.62	5.742%	$108.5124	$108.51	$108.50	$108.50
Purchase #3	$139.56	8.431%	$151.3263	$151.33	$151.35	$151.30
Purchase #4	$182.59	9.135%	$199.2696	$199.27	$199.25	$199.30
Purchase #5	$19.38	5.432%	$20.4327	$20.43	$20.45	$20.40
Purchase #6	$125.36	13.755%	$142.6033	$142.60	$142.60	$142.60
Purchase #7	$48.60	9.622%	$53.2763	$53.28	$53.30	$53.30
7 purchase totals =	$805.76		$886.8965	$886.90	$886.95	$886.90