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	$247.90	9.352%	$271.0836	$271.08	$271.10	$271.10
Purchase #2	$250.84	10.830%	$278.006	$278.01	$278.00	$278.00
Purchase #3	$73.41	10.207%	$80.903	$80.90	$80.90	$80.90
Purchase #4	$138.40	5.383%	$145.8501	$145.85	$145.85	$145.90
Purchase #5	$19.77	8.589%	$21.468	$21.47	$21.45	$21.50
Purchase #6	$112.90	9.427%	$123.5431	$123.54	$123.55	$123.50
Purchase #7	$232.30	10.829%	$257.4558	$257.46	$257.45	$257.50
7 purchase totals =	$1,075.52		$1,178.3096	$1,178.31	$1,178.30	$1,178.40