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	$107.78	3.251%	$111.2839	$111.28	$111.30	$111.30
Purchase #2	$36.35	7.799%	$39.1849	$39.18	$39.20	$39.20
Purchase #3	$99.72	3.837%	$103.5463	$103.55	$103.55	$103.50
Purchase #4	$109.59	9.627%	$120.1402	$120.14	$120.15	$120.10
Purchase #5	$51.57	9.427%	$56.4315	$56.43	$56.45	$56.40
Purchase #6	$168.69	5.163%	$177.3995	$177.40	$177.40	$177.40
Purchase #7	$250.64	12.782%	$282.6768	$282.68	$282.70	$282.70
7 purchase totals =	$824.34		$890.6631	$890.66	$890.75	$890.60