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	$103.63	11.362%	$115.4044	$115.40	$115.40	$115.40
Purchase #2	$94.86	5.296%	$99.8838	$99.88	$99.90	$99.90
Purchase #3	$103.25	9.610%	$113.1723	$113.17	$113.15	$113.20
Purchase #4	$80.28	12.662%	$90.4451	$90.45	$90.45	$90.40
Purchase #5	$159.47	6.231%	$169.4066	$169.41	$169.40	$169.40
Purchase #6	$58.71	11.698%	$65.5779	$65.58	$65.60	$65.60
Purchase #7	$182.42	6.327%	$193.9617	$193.96	$193.95	$194.00
7 purchase totals =	$782.62		$847.8518	$847.85	$847.85	$847.90