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	$147.80	9.166%	$161.3473	$161.35	$161.35	$161.30
Purchase #2	$66.94	12.145%	$75.0699	$75.07	$75.05	$75.10
Purchase #3	$80.52	3.161%	$83.0652	$83.07	$83.05	$83.10
Purchase #4	$52.56	13.240%	$59.5189	$59.52	$59.50	$59.50
Purchase #5	$113.43	8.814%	$123.4277	$123.43	$123.45	$123.40
Purchase #6	$77.41	7.791%	$83.441	$83.44	$83.45	$83.40
Purchase #7	$112.74	9.735%	$123.7152	$123.72	$123.70	$123.70
7 purchase totals =	$651.40		$709.5852	$709.60	$709.55	$709.50