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	$27.45	7.120%	$29.4044	$29.40	$29.40	$29.40
Purchase #2	$13.56	11.751%	$15.1534	$15.15	$15.15	$15.20
Purchase #3	$23.29	10.760%	$25.796	$25.80	$25.80	$25.80
Purchase #4	$60.54	11.685%	$67.6141	$67.61	$67.60	$67.60
Purchase #5	$158.38	3.626%	$164.1229	$164.12	$164.10	$164.10
Purchase #6	$115.73	9.534%	$126.7637	$126.76	$126.75	$126.80
Purchase #7	$92.69	11.640%	$103.4791	$103.48	$103.50	$103.50
7 purchase totals =	$491.64		$532.3336	$532.32	$532.30	$532.40